Enabling and disabling anti-tachyarrhythmia pacing in a concomitant medical device system

ABSTRACT

An implantable medical device comprising a signal generator configured to generate and deliver anti-tachyarrhythmia pacing (ATP) to a heart of a patient and processing circuitry. The processing circuitry is configured to detect an enable event, responsive to detecting the enable event, enable the delivery of ATP by the signal generator, detect a disable event indicating that another implantable medical device cannot be relied upon to deliver an anti-tachyarrhythmia shock, and responsive to detecting the disable event, disable delivery of ATP.

TECHNICAL FIELD

This disclosure relates generally to medical devices and, moreparticularly, to medical devices, medical device systems, and methodsfor treating cardiac arrhythmias.

BACKGROUND

Implantable cardioverter defibrillators (ICDs) and implantableartificial pacemakers may provide cardiac pacing therapy to a patient'sheart when the natural pacemaker and/or conduction system of the heartfails to provide synchronized atrial and ventricular contractions atrates and intervals sufficient to sustain healthy patient function. Suchantibradycardial pacing may provide relief from symptoms, or even lifesupport, for a patient. Cardiac pacing may also provide electricaloverdrive stimulation, e.g., anti-tachyarrhythmia pacing (ATP) therapy,to suppress or convert tachyarrhythmias, again supplying relief fromsymptoms and preventing or terminating arrhythmias that could lead tosudden cardiac death.

SUMMARY

Some extracardiovascular defibrillators, such as subcutaneous ICDs, mayhave limited capabilities to provide anti-tachyarrhythmia pacing (ATP)therapies to terminate some types of tachyarrhythmia episodes. In suchsituations, an additional pacing device may be used that is capable ofdelivering ATP therapy. The systems and methods described herein includetechniques that may be used to enable and disable delivery of ATPtherapy in such a pacing device, depending on whether a device capableof delivering an anti-tachyarrhythmia shock is considered to beavailable.

In one example, this disclosure is directed to a method comprisingdetecting, by an implantable medical device configured to deliver ATP toa heart of a patient, an enable event. The method further comprises,responsive to detecting the enable event, enabling, by the implantablemedical device, the delivery of ATP. The method further comprisesdetecting, by the implantable medical device, a disable event indicatingthat another implantable medical device cannot be relied upon to deliveran anti-tachyarrhythmia shock. The method further comprises, responsiveto detecting the disable event, disabling, by the implantable medicaldevice, delivery of ATP.

In another example, this disclosure is directed to an implantablemedical device comprising signal generation circuitry configured togenerate and deliver ATP to a heart of a patient and processingcircuitry. The processing circuitry is configured to detect an enableevent, responsive to detecting the enable event, enable the delivery ofATP by signal generation circuitry, detect a disable event indicatingthat another implantable medical device cannot be relied upon to deliveran anti-tachyarrhythmia shock and responsive to detecting the disableevent, disable delivery of ATP.

In a further example, this disclosure is directed to a non-transitorycomputer-readable storage medium encoded with instructions that, whenexecuted by processing circuitry an implantable medical deviceconfigured to deliver ATP to a heart of a patient, cause the processorto detect an enable event, responsive to detecting the enable event,enable the delivery of ATP by the implantable medical device, detect adisable event indicating that another implantable medical device cannotbe relied upon to deliver an anti-tachyarrhythmia shock, and responsiveto detecting the disable event, disable delivery of ATP.

In a further example, this disclosure is directed to a system comprisingan extracardiovascular medical device configured for extracardiovascularimplantation within a patient and configured to deliver ananti-tachyarrhythmia shock, and an intracardiac pacing device. Theintracardiac pacing device comprises a housing configured forimplantation within a heart of the patient, a plurality of electrodesconfigured for implantation in the heart, signal generation circuitrywithin the housing, signal generation circuitry configured to deliverATP to the heart via the plurality of electrodes, communicationcircuitry within the housing and configured to receive enable signalsfrom an external device via wireless communication or telemetry, andprocessing circuitry within the housing. The processing circuitry isconfigured to detect receipt of an enable signal from the externaldevice, responsive to detecting the receipt of the enable signal, enablethe delivery of ATP by signal generation circuitry, responsive todetecting receipt of the enable signal, start a timer, responsive todetecting receipt of each of one or more subsequent enable signals,restart the timer, and responsive to detecting expiration of the timer,disable delivery of ATP.

In a further example, this disclosure is directed to a method comprisingevaluating a medical device system implanted in a patient, the medicaldevice system including an implanted pacing device and an implantedcardiac defibrillator. The method further comprises performing anassessment of the implanted cardiac defibrillator to determine a timeperiod during which the implanted cardiac defibrillator is expected tocontinue operate properly. The method further comprises sending anenable command to the implanted pacing device, the enable commandincluding information derived from the time period during which theimplanted cardiac defibrillator is expected to operate properly.

This summary is intended to provide an overview of the subject matterdescribed in this disclosure. It is not intended to provide an exclusiveor exhaustive explanation of the apparatus and methods described indetail within the accompanying drawings and description below. Thedetails of one or more aspects of the disclosure are set forth in theaccompanying drawings and the description below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an example front view of a patient implanted with an examplemedical device system that includes an extracardiovascular ICD systemand a intracardiac pacing device (IPD) implanted within a cardiacchamber of the patient in accordance with one or more aspects of thepresent disclosure.

FIG. 2A is an example front view of a patient implanted with anotherexample medical device system that includes an extracardiovascular ICDsystem and a intracardiac pacing device (IPD) implanted within a cardiacchamber of the patient in accordance with one or more aspects of thepresent disclosure.

FIG. 2B is an example side view of a patient implanted with the examplemedical device system of FIG. 2A in accordance with one or more aspectsof the present disclosure.

FIG. 2C is an example transverse view of a patient implanted with theexample medical device system of FIG. 2A in accordance with one or moreaspects of the present disclosure.

FIG. 3 is a conceptual drawing illustrating the example IPD of FIG. 1 inaccordance with one or more aspects of the present disclosure.

FIG. 4 is a functional block diagram illustrating an exampleconfiguration of the IPD of FIG. 1 in accordance with one or moreaspects of the present disclosure.

FIG. 5 is a functional block diagram illustrating an exampleconfiguration of the ICD of FIG. 1 in accordance with one or moreaspects of the present disclosure.

FIG. 6 is a functional block diagram illustrating an exampleconfiguration of the external device of FIG. 1 in accordance with one ormore aspects of the present disclosure.

FIG. 7 is a functional block diagram illustrating an example networkincluding the external device of FIG. 1 in accordance with one or moreaspects of the present disclosure.

FIG. 8 is a flow diagram illustrating example operations of the exampleIPD of FIG. 1 and FIG. 4 in accordance with one or more aspects of thepresent disclosure.

FIG. 9 is a flow diagram illustrating example operations of the exampleIPD of FIG. 1 and FIG. 4 in accordance with one or more aspects of thepresent disclosure.

FIG. 10A is a flow diagram illustrating example operations of theexample IPD of FIG. 1 and FIG. 4 in accordance with one or more aspectsof the present disclosure.

FIG. 10B is a flow diagram illustrating example operations of theexample IPD of FIG. 1 and FIG. 4 in accordance with one or more aspectsof the present disclosure.

FIG. 11 is a flow diagram illustrating example operations of the exampleIPD of FIG. 1 and FIG. 4 in accordance with one or more aspects of thepresent disclosure.

FIG. 12 is a flow diagram illustrating example operations of the examplemedical device system of FIG. 1 in accordance with one or more aspectsof the present disclosure.

DETAILED DESCRIPTION

In general, this disclosure describes subject matter relating to thedelivery of anti-tachyarrhythmia pacing (ATP) therapies in a concomitantcardiac medical device system. In accordance with one or more aspects ofthe present disclosure, techniques are described that may help ensurethat a pacing device provide ATP therapy, in some examples, only whenanother device capable of delivering an anti-tachyarrhythmia shock isavailable. In the following description, references are made toillustrative examples. It is understood that other examples may beutilized without departing from the scope of the disclosure.

FIG. 1 is a front view of an example medical device system 8 thatincludes an extracardiovascular ICD system 30 and IPD 16 implantedwithin a patient. In the example of FIG. 1, extracardiovascular ICDsystem 30 includes ICD 9 coupled to a cardiac defibrillation lead 25,which extends subcutaneously above the ribcage from ICD 9. In theillustrated example, defibrillation lead 25 extends toward a center ofthe torso of patient 14, bends or turns near the center of the torso,and extends subcutaneously superior above the ribcage and/or sternum 22.Defibrillation lead 25 may be offset laterally to the left or the rightof sternum 22 or located over sternum 22. Defibrillation lead 25 mayextend substantially parallel to sternum 22 or be angled lateral fromthe sternum at either the proximal or distal end.

Defibrillation lead 25 includes an insulative lead body having aproximal end that includes a connector 34 configured to be connected toICD 9 and a distal portion that includes one or more electrodes.Defibrillation lead 25 also includes one or more conductors that form anelectrically conductive path within the lead body and interconnect theelectrical connector and respective ones of the electrodes. In theexample of FIG. 1, defibrillation lead 25 includes a singledefibrillation electrode 28 toward the distal portion of defibrillationlead 25, e.g., toward the portion of defibrillation lead 25 extendingalong sternum 22. Defibrillation lead 25 is placed along sternum suchthat a therapy vector between defibrillation electrode 28 and a housingelectrode formed by or on ICD 9 (or other second electrode of thetherapy vector) is substantially across a ventricle of heart 26.

Defibrillation lead 25 may also include one or more sensing electrodes,such as sensing electrodes 32 a and 32 b, located along the distalportion of defibrillation lead 25. In the example illustrated in FIG. 1,sensing electrodes 32 a and 32 b are separated from one another bydefibrillation electrode 28. In other examples, however, sensingelectrodes 32 a and 32 b may be both distal of defibrillation electrode28 or both proximal of defibrillation electrode 28. In other examples,lead 25 may include more or fewer electrodes at various locationsproximal and/or distal to defibrillation electrode 28, and lead 25 mayinclude multiple defibrillation electrodes, e.g., defibrillationelectrodes 28 a and 28 b. IPD 16 may be configured to detect shocksdelivered by ICD 9 via lead 25.

FIG. 2A, FIG. 2B, and FIG. 2C are conceptual diagrams illustratingvarious views of another example cardiac medical device system 8implanted within a patient 14. Components with like numbers in FIG. 1,FIG. 2A, FIG. 2B, and FIG. 2C may be similarly configured and mayprovide similar functionality. With reference to FIG. 2A, cardiac system8 includes an extracardiovascular ICD system 30 implanted in patient 14and an intracardiac pacing device (IPD) 16 implanted within heart 26 ofpatient 14. FIG. 2A is a front view of a patient implanted with thecardiac system 8 of FIG. 2A. FIG. 2B is a side view of the patientimplanted with the cardiac system 8 of FIG. 2A. FIG. 2C is a transverseview of the patient implanted with the cardiac system 8 of FIG. 2A.Medical device system 8 as illustrated in FIG. 2A, FIG. 2B, and FIG. 2Cmay be configured to perform one or more of the techniques describedherein with respect to medical device system 8 of FIG. 1.

Referring again to FIG. 2A, ICD system 30 includes an implantablecardiac defibrillator (ICD) 9 connected to at least one implantablecardiac defibrillation lead 25. ICD 9 is configured to deliverhigh-energy cardioversion or defibrillation pulses to a patient's heartwhen atrial or ventricular fibrillation is detected. Cardioversionshocks are typically delivered in synchrony with a detected R-wave whenfibrillation detection criteria are met. Defibrillation pulses aretypically delivered when fibrillation criteria are met, and the R-wavecannot be discerned from signals sensed by ICD 9.

ICD 9 of FIG. 2A is implanted subcutaneously or submuscularly on theleft side of patient 14 above the ribcage. Unlike defibrillation lead 25of FIG. 1, defibrillation lead 25 of FIG. 2A may be implanted at leastpartially in a substernal location in FIG. 2A, e.g., between the ribcageand/or sternum 22 and heart. In one such configuration, a proximalportion of lead 25 extends subcutaneously from ICD 9 toward the sternumand a distal portion of lead 25 extends superior under or below thesternum 22 in the anterior mediastinum 36. The anterior mediastinum 36is bounded laterally by the pleurae 39 (see FIG. 2C), posteriorly by thepericardium, and anteriorly by the sternum 22. In some instances, theanterior wall of the anterior mediastinum may also be formed by thetransversus thoracis and one or more costal cartilages. The anteriormediastinum includes a quantity of loose connective tissue (such asareolar tissue), some lymph vessels, lymph glands, substernalmusculature (e.g., transverse thoracic muscle), branches of the internalthoracic artery, and the internal thoracic vein. In one example, thedistal portion of lead 25 extends along the posterior side of thesternum 22 substantially within the loose connective tissue and/orsubsternal musculature of the anterior mediastinum. Lead 25 may be atleast partially implanted in other intrathoracic locations, e.g., othernon-vascular, extra-pericardial locations, including the gap, tissue, orother anatomical features around the perimeter of and adjacent to, butnot attached to, the pericardium or other portion of the heart and notabove the sternum 22 or ribcage.

In other examples, lead 25 may be implanted at other extracardiovascularlocations. For example, defibrillation lead 25 may extend subcutaneouslyabove the ribcage from ICD 9 toward a center of the torso of patient 14,bend or turn near the center of the torso, and extend subcutaneouslysuperior above the ribcage and/or sternum 22, similar to that shown inFIG. 1. Defibrillation lead 25 may be offset laterally to the left orthe right of the sternum 22 or located over the sternum 22.Defibrillation lead 25 may extend substantially parallel to the sternum22 or be angled lateral from the sternum 22 at either the proximal ordistal end.

Defibrillation lead 25 of FIG. 2A includes an insulative lead bodyhaving a proximal end that includes a connector configured to beconnected to ICD 9 and a distal portion that includes one or moreelectrodes. Defibrillation lead 25 also includes one or more conductorsthat form an electrically conductive path within the lead body andinterconnect the electrical connector and respective ones of theelectrodes.

Defibrillation lead 25 of FIG. 2A includes a defibrillation electrodethat includes two sections or segments 28 a and 28 b, collectively (oralternatively) defibrillation electrodes 28. The defibrillationelectrodes 28 of FIG. 2A are toward the distal portion of defibrillationlead 25, e.g., toward the portion of defibrillation lead 25 extendingalong the sternum 22. Defibrillation lead 25 of FIG. 2A is placed belowand/or along sternum 22 such that a therapy vector betweendefibrillation electrodes 28 a or 28 b and a housing electrode formed byor on ICD 9 (or other second electrode of the therapy vector) issubstantially across a ventricle of heart 26. The therapy vector may, inone example, be viewed as a line that extends from a point ondefibrillation electrodes 28 (e.g., a center of one of thedefibrillation electrode sections 28 a or 28 b) to a point on thehousing electrode of ICD 9. Defibrillation electrode 28 of FIG. 2A may,in one example, be an elongated coil electrode.

Defibrillation lead 25 may also include one or more sensing electrodes,such as sensing electrodes 32 a and 32 b, located along the distalportion of defibrillation lead 25. In the example illustrated in FIG. 2Aand FIG. 2B, sensing electrodes 32 a and 32 b are separated from oneanother by defibrillation electrode 28 a. In other examples, however,sensing electrodes 32 a and 32 b may be both distal of defibrillationelectrode 28 or both proximal of defibrillation electrode 28. In otherexamples, lead 25 may include more or fewer electrodes at variouslocations proximal and/or distal to defibrillation electrode 28. In thesame or different examples, ICD 9 may include one or more electrodes onanother lead (not shown).

ICD system 30 may sense electrical signals via one or more sensingvectors that include combinations of electrodes 32 a and 32 b and thehousing electrode of ICD 9. For example, ICD 9 may obtain electricalsignals sensed using a sensing vector between electrodes 32 a and 32 b,obtain electrical signals sensed using a sensing vector betweenelectrode 32 b and the conductive housing electrode of ICD 9, obtainelectrical signals sensed using a sensing vector between electrode 32 aand the conductive housing electrode of ICD 9, or a combination thereof.In some instances, ICD 9 may sense cardiac electrical signals using asensing vector that includes one of the defibrillation electrodesections 28 a and 28 b (or electrode 28 in FIG. 1) and one of sensingelectrodes 32 a and 32 b or the housing electrode of ICD 9.

The sensed electrical intrinsic signals may include electrical signalsgenerated by cardiac muscle and indicative of depolarizations andrepolarizations of heart 26 at various times during the cardiac cycle.Additionally, the sensed electrical signals may also include electricalsignals, e.g., pacing pulses, generated and delivered to heart 26 by IPD16. ICD 9 analyzes the electrical signals sensed by the one or moresensing vectors to detect tachyarrhythmia, such as ventriculartachycardia or ventricular fibrillation. In response to detecting thetachyarrhythmia, ICD 9 may begin to charge a storage element, such as abank of one or more capacitors, and, when charged, deliver one or moredefibrillation pulses via defibrillation electrodes 28 (e.g., 28, 28 a,28 b) of defibrillation lead 25 if the tachyarrhythmia is still present.

In the example of FIG. 2A, IPD 16 is implanted within the rightventricle of heart 26 to sense electrical activity of heart 26 anddeliver pacing therapy, e.g., anti-tachycardia pacing (ATP) therapy,bradycardia pacing therapy, and/or post-shock pacing, to heart 26. IPD16 may be attached to an interior wall of the right ventricle of heart26 via one or more fixation elements that penetrate the tissue. Thesefixation elements may secure IPD 16 to the cardiac tissue and retain anelectrode (e.g., a cathode or an anode) in contact with the cardiactissue. However, in other examples, system 8 may include additionalpacing devices 16 within respective chambers of heart 26 (e.g., right orleft atrium and/or left ventricle). In further examples, IPD 16 may beattached to an external surface of heart 26 (e.g., in contact with theepicardium) such that IPD 16 is disposed outside of heart 26.

IPD 16 may be capable sensing electrical signals using the electrodescarried on the housing of IPD 16. These electrical signals may beelectrical signals generated by cardiac muscle and indicative ofdepolarizations and repolarizations of heart 26 at various times duringthe cardiac cycle. IPD 16 may analyze the sensed electrical signals todetect tachyarrhythmias, such as ventricular tachycardia or ventricularfibrillation. In response to detecting the tachyarrhythmia, IPD 16 may,e.g., depending on the type of tachyarrhythmia, begin to deliver ATPtherapy via the electrodes of IPD 16. In addition to or instead of ATPtherapy, IPD 16 may also deliver bradycardia pacing therapy andpost-shock pacing.

Cardiac IPD 16 and ICD system 30 may be configured to operate completelyindependent of one another. In such a case, IPD 16 and ICD system 30 arenot capable of establishing telemetry or other communication sessionswith one another to exchange information about sensing and/or therapyusing one-way or two-way communication. Instead, each of IPD 16 and ICDsystem 30 analyze the data sensed via their respective electrodes tomake tachyarrhythmia detection and/or therapy decisions. As such, eachdevice does not know if the other will detect the tachyarrhythmia, if orwhen it will provide therapy, and the like.

During a tachyarrhythmia that could be treated with either ATP or ananti-tachyarrhythmia shock, e.g., cardioversion or defibrillation shock,it is important to ensure that anti-tachyarrhythmia therapies do notoverlap or that ATP therapy does not take place after the defibrillationpulse. Applying ATP after a defibrillation pulse could be pro-arrhythmicand present a hazard to the patient. Moreover, it would be desirable forIPD 16 to deliver post-shock pacing after delivery of acardioversion/defibrillation pulse. Systems could be designed to providedevice-to-device communication between ICD system 30 and IPD 16, butthis may add complexity to the system and not be highly effective orfast enough to prevent unwanted ATP therapies post defibrillation pulseor too slow to initiate post-shock pacing therapies. In some examplesdescribed herein, IPD 16 may be configured to detectanti-tachyarrhythmia shocks delivered by ICD 9, which improve thecoordination of therapy between subcutaneous ICD 9 and IPD 16 withoutrequiring device-to-device communication. Although ICD 9 and IPD 16 maynot require or utilize device-to-device communication to coordinatetachyarrhythmia therapy, the devices may still communicate with oneanother for other reasons, as described below in further detail.

Although FIG. 2A is shown or described in the context of a substernalICD system 30 and a IPD 16, techniques in accordance with one or moreaspects of the present disclosure may be applicable to other coexistentsystems. For example, an ICD system may include a lead having a distalportion that is implanted subcutaneously above the sternum (or otherlocation) instead of being implanted substernally, in a manner similarto that shown in FIG. 1. As another example, instead of an intracardiacpacing device, a pacing system may be implanted having a pacemaker andone or more leads connected to and extending from the pacemaker into oneor more chambers of the heart or attached to the outside of the heart toprovide pacing therapy to the one or more chambers. As such, theexamples of FIG. 1, FIG. 2A, FIG. 2B, and FIG. 2C are illustrated forexample purposes only and should not be considered limiting of thetechniques described herein.

External device 21 may be configured to communicate with one or both ofICD system 30 and IPD 16. In examples where external device 21 onlycommunicates with one of ICD system 30 and IPD 16, the non-communicativedevice may receive instructions from or transmit data to the device incommunication with device 21. In some examples, device 21 comprises ahandheld computing device, computer workstation, or networked computingdevice. Device 21 may include a user interface that receives input froma user. In other examples, the user may also interact with device 21remotely via a networked computing device. The user may interact withdevice 21 to communicate with IPD 16 and/or ICD system 30. For example,the user may interact with device 21 to send an interrogation requestand retrieve therapy delivery data, update therapy parameters thatdefine therapy, manage communication between IPD 16 and/or ICD system30, or perform any other activities with respect to IPD 16 and/or ICDsystem 30. Although the user is a physician, technician, surgeon,electrophysiologist, or other healthcare professional, the user may bepatient 14 in some examples.

Device 21 may also allow the user to define how IPD 16 and/or ICD system30 senses electrical signals (e.g., ECGs), detects arrhythmias (e.g.,tachyarrhythmias), delivers therapy, and communicates with other devicesof system 8. For example, device 21 may be used to changetachyarrhythmia detection parameters. In another example, device 21 maybe used to manage therapy parameters that define therapies such asanti-tachyarrhythmia shocks and/or ATP. In examples in which IPD 16 andICD system 30 communicate, device 21 may be used to alter communicationprotocols between IPD 16 and ICD system 30. For example, device 21 mayinstruct IPD 16 and/or ICD system 30 to switch between one-way andtwo-way communication and/or change which of IPD 16 and/or ICD system 30are tasked with initial detection of arrhythmias.

Device 21 may communicate with IPD 16 and/or ICD system 30 via wirelesscommunication using any techniques known in the art. Examples ofcommunication techniques may include, for example, proprietary andnon-proprietary radiofrequency (RF) telemetry, inductive telemetry,acoustics, and TCC, but other techniques are also contemplated. DuringTCC (tissue conduction communication), current is driven through thetissue between two or more electrodes of a transmitting device. Theelectrical signal spreads and can be detected at a distance by measuringthe voltage generated between two electrodes of a receiving device. Insome examples, device 21 may include a programming head that may beplaced proximate to the patient's body near the IPD 16 and/or ICD system30 implant site in order to improve the quality or security ofcommunication between IPD 16 and/or ICD system 30 and device 21.

IPD 16 may be configured to adjust cardiac therapy based on theapplication of anti-tachyarrhythmia shock therapy by ICD 9. It may beuseful that IPD 16 knows when ICD 9 has delivered tachyarrhythmia shocktherapy. In response to the delivery of the shock, IPD 16 may terminateATP and activate post-shock pacing.

In some examples, IPD 16 and ICD system 30 may engage in communicationto facilitate the appropriate detection of arrhythmias and/or deliveryof anti-tachycardia therapy. Anti-tachycardia therapy may includeanti-tachyarrhythmia shocks (e.g., cardioversion or defibrillationpulses) and/or anti-tachycardia pacing (ATP). The communication mayinclude one-way communication in which one device is configured totransmit communication messages and the other device is configured toreceive those messages. The communication may instead include two-waycommunication in which each device is configured to transmit and receivecommunication messages. Although the examples below describe detectionof tachyarrhythmias and the delivery of anti-tachyarrhythmia shocksand/or ATP, IPD 16 and ICD system 30 may be configured to communicatewith each other and provide alternative electrical stimulationtherapies. Two-way communication and coordination of the delivery ofpatient therapies between IPD 16 and ICD system 30 is described incommonly-assigned U.S. patent application Ser. No. 13/756,085, titled,“SYSTEMS AND METHODS FOR LEADLESS PACING AND SHOCK THERAPY,” filed Jan.31, 2013, the entire content of which is incorporated by referenceherein.

In combination with, or as an alternative to, communication between IPD16 and ICD system 30, IPD 16 may be configured to detect ananti-tachyarrhythmia shock delivered by ICD system 30 or an externaldefibrillator according to the detection of an electrical signal acrosstwo or more electrodes of IPD 16. IPD 16 may be configured to detect ananti-tachyarrhythmia shock based on electrical characteristics of theanti-tachyarrhythmia shock. Even though different defibrillation devicesmay provide different waveforms, including different pulse durations andamplitudes, defibrillation pulses generally have electrical signalcharacteristics such that detection of an anti-tachyarrhythmia shock canoccur even without prior knowledge as to an anti-tachyarrhythmia shockwaveform of an implanted or external defibrillator. In this manner, IPD16 may coordinate the delivery of cardiac stimulation therapy, includingthe termination of ATP and the initiation of the delivery of post-shockpacing, with the application of an anti-tachyarrhythmia shock merelythrough the detection of defibrillation pulses and without the need tocommunicate with the defibrillation device applying theanti-tachyarrhythmia shock.

In some examples, IPD 16 detects the anti-tachyarrhythmia shock bymeasuring the voltage across the electrode inputs of the implanteddevice. IPD 16 may detect one or more signal characteristics of ananti-tachyarrhythmia shock including: detection of the high amplitudelevel of an anti-tachyarrhythmia shock, detection of a high slew rate ofthe leading and trailing edges, and detection of a large post-shockpolarization change. Detection of more than one signal characteristicmay improve sensitivity and/or specificity. For example, IPD 16 maydetect a high level of an anti-tachyarrhythmia shock in combination withone or both of the detection of a high slew rate of the leading andtrailing edges, and the detection of a large post-shock polarizationchange.

In one example, IPD 16 may be configured to receive an indication of adetected cardiac arrhythmia eligible for anti-tachyarrhythmia shocktherapy. IPD 16 may include a set of electrodes configured to beimplanted within or near heart 26 of patient 14. In response toreceiving the indication of the tachyarrhythmia, IPD 16 may enable shockdetection circuitry of IPD 16 configured to detect delivery ofanti-tachyarrhythmia shock therapy. The shock detection circuitry maythen detect delivery of anti-tachyarrhythmia shock therapy by measuringthe voltage across the electrode inputs (e.g., detect that the shock hasbeen delivered). The shock detection circuitry may apply one or more ofthree general techniques for detection of an anti-tachyarrhythmia shock:detection of the high level of an anti-tachyarrhythmia shock, detectionof a high slew rate of the leading and trailing edges, and detection ofa large post-shock polarization change. Each technique looks for adifferent electrical signal characteristic. The three techniques may becombined to improve sensitivity and/or specificity. For example, thehigh level of an anti-tachyarrhythmia shock may be combined with one orboth of the detection of a high slew rate of the leading and trailingedges, and the detection of a large post-shock polarization change.

In response to detection of the anti-tachyarrhythmia shock, the IPD 16may abort and/or temporarily suspend the delivery of ATP and to activatepost-shock pacing, such as VVI (Ventricular sensing, Ventricular pacing,Inhibited pacing when activity sensed) post-shock pacing. ATP may remainsuspended temporarily following an anti-tachyarrhythmia shock to insurethat the relatively higher-rate pacing pulses will not induce anotherarrhythmia. Additionally, post-shock pacing may be used to insure pacingsupport if the patient's heart does not begin to beat normallyimmediately following an anti-tachyarrhythmia shock. The pacing devicemay deliver post-shock pacing with a higher than normal pulse amplitudeand pulse width (relative to typical cardiac pacing) to minimize therisk of loss of capture following an anti-tachyarrhythmia shock. Ahigher capture threshold may occur as a result of tissue stunning due toelevated current in the myocardial tissue from the anti-tachyarrhythmiashock delivery. A higher threshold may also occur as a result ofphysiological changes in the tissue resulting from lack of blood flow tothe myocardium during ventricular fibrillation (VF). Furthermore, afteran anti-tachyarrhythmia shock there can be increased polarization at thelead interface resulting in the need for a higher voltage to overcomethe lead polarization.

In one example, IPD 16 may deliver post-shock pacing to heart 26 via atleast a subset of the set of electrodes of IPD 16. In some examples, IPD16 may deliver the post-shock pacing after entering a post-shock pacingmode in response to detecting the shock. In some examples, IPD 16 mayuse a timer to determine when a predetermined time has elapsed, duringwhich the shock should have been delivered. IPD 16 may begin post-shockpacing after the predetermined period has elapsed and/or stop post-shockpacing.

IPD 16 may receive the indication of the detected cardiactachyarrhythmia in a variety of ways. For example, IPD 16 may sense, viaat least a subset of the set of electrodes, an electrical signal fromheart 26. IPD 16 may then detect, from the electrical signal, a cardiactachyarrhythmia eligible for anti-tachyarrhythmia shock therapy. In thismanner, IPD 16 may receive the indication of the detected arrhythmia viadirect detection of the arrhythmia at IPD 16. In another example, ICDsystem 30 may be configured to transmit a communication including theindication to IPD 16. The indication of the detected arrhythmia may thusbe received from ICD system 30, for example. IPD 16 may receive acommunication from ICD system 30 indicating that a cardiac arrhythmiawas detected by ICD system 30. Alternatively, IPD 16 may receive acommunication from ICD system 30 indicating that a shock is impending.

Detection of the anti-tachyarrhythmia shock may be used to abort and/ortemporarily suspend the delivery of ATP and to activate post-shockpacing, such as VVI post-shock pacing. ATP may be temporarily suspendedfollowing an anti-tachyarrhythmia shock to insure that the pacing pulseswill not induce another arrhythmia. For example, ATP may be temporarilysuspended following an anti-tachyarrhythmia shock until the currentarrhythmia has been terminated or until a short period of time haselapsed to prevent interfering with the subcutaneous ICD.

In addition to the delivery of ATP, IPD 16 may be configured to deliverpost-shock pacing to heart 26. After delivery of an anti-tachyarrhythmiashock, heart 26 may benefit from pacing to return to a normal sinusrhythm (e.g., if heart 26 has developed bradycardia or asystole) orotherwise recover from receiving the shock. In some examples, IPD 16and/or ICD system 30 may be configured to detect bradycardia orasystole. In some examples, this post-shock pacing may be automaticallydelivered in response to the IPD 16 detecting that a shock wasdelivered. Post-shock pacing may be used to ensure pacing support if thepatient's heart does not begin to beat normally immediately following ananti-tachyarrhythmia shock. A higher than normal amplitude and pulsewidth is commonly used to minimize the risk of loss of capture followingan anti-tachyarrhythmia shock. A higher capture threshold may occur as aresult of tissue stunning due to elevated current in the myocardialtissue from the anti-tachyarrhythmia shock delivery. A higher thresholdmay also occur as a result of physiological changes in the tissueresulting from lack of blood flow to the myocardium during VF.Furthermore, after an anti-tachyarrhythmia shock there can be increasedpolarization at the lead interface resulting in the need for a highervoltage to overcome the lead polarization.

In some examples, IPD 16 may enable the shock detection circuitry whenATP is delivered to heart 26, in anticipation of a shock. In someexamples, IPD 16 may enable the shock detection circuitry in response todetecting a fast rate, such as a tachyarrhythmia (e.g., whencommunication between IPD 16 and ICD system 30 is not present or isunreliable). The tachyarrhythmia may be detected based on sensedelectrical signals and/or mechanical signals from heart 26. In someexamples, the shock detection circuitry may be disabled until anindication of an arrhythmia is terminated or impending shock isreceived.

IPD 16 may also be configured to disable the shock detection circuitry.For example, IPD 16 may be configured to track a period of timefollowing detection of delivery of anti-tachyarrhythmia shock therapy.The period of time may be a predetermined period of time and/or trackedwith a timer, for example. IPD 16 may also determine that the period oftime exceeds a timeout threshold, and, in response to the determination,disable the shock detection circuitry. IPD 16 may disable the shockdetection circuitry when not needed to conserve battery power, forexample.

IPD 16 may also re-start post-shock pacing if additional shocks aredetected. For example, IPD 16 may be configured to detect a first shockand begin delivery of the post-shock pacing if needed (e.g., bradycardiaor systole has been detected). IPD 16 may subsequently detect thedelivery of a second shock, and, in response to the detection of thesecond shock, re-start delivery of the post-shock pacing if needed. IPD16 may continue to re-start post-shock pacing as long as additionalshocks are delivered. However, IPD 16 may be configured to stopre-starting post-shock pacing after a predetermined number of shocks, orin response to ICD system 30 transmitting a message instructing IPD 16to stop delivery of post-shock pacing. IPD 16 and/or ICD system 30 mayimplement an intrinsic beat detector or other algorithm to distinguishbetween intrinsic beats and potential artifacts caused by pacing and/orshock therapy. IPD 16 may also deliver ATP upon detection of atachyarrhythmia, and terminate ATP if a defibrillation pulse isdetected. IPD 16 may initiate post-shock pacing and/or, upon detectionof additional tachyarrhythmia following the shock, resume ATP.

In some examples, IPD 16 may terminate post-shock pacing in response tovarious indicators. For example, IPD 16 may track a period of timefollowing the start of post-shock pacing. IPD 16 may then determine thatthe period of time exceeds a timeout threshold. For example, IPD 16 mayuse a timer to track this period of time. In response to thedetermination, IPD 16 may terminate delivery of post-shock pacing. Inother examples, IPD 16 may terminate post-shock pacing after delivery ofa predetermined number of pacing pulses. Alternatively, IPD 16 mayterminate post-shock pacing in response to detection of a normal sinusrhythm or receiving a communication from ICD system 30 instructing IPD16 to terminate post-shock pacing.

Although IPD 16 is generally described as delivering post-shock pacing,in other examples, different implanted devices may provide post-shockpacing. For example, IPD 16 may be configured to deliver ATP, but adifferent IPD implanted in a different chamber of heart 26 may beconfigured to detect a shock and deliver the post-shock pacing to heart26. In other examples, the implanted device delivering post-shock pacingmay not be an intracardiac pacing device or leadless pacing device. Forexample, an implantable pacing device, separate from an ICD deliveringthe anti-tachyarrhythmia shock, may include one or more leads fordelivering post-shock pacing therapy to one or more locations of heart26. As another example, an ICD delivering the anti-tachyarrhythmia shockmay deliver post-shock pacing, whereas IPD is configured to provide ATP,and not post-shock pacing.

Some ICD systems, such as ICD system 30 in FIG. 1, may have limitedcapabilities to deliver anti-tachycardia pacing and post-shock pacing aswell as conventional brady pacing therapy. In some examples, anotherdevice, such as IPD 16, may be used to deliver such pacing therapies. Inparticular, delivery of anti-tachycardia pacing (ATP) therapy by adevice such as IPD 16 may be helpful in treating tachycardia episodes.However, when using ATP therapy to treat a tachycardia episode, theremay be risks associated with delivering ATP therapy. For example,although the risk may be small, it is possible that delivery of ATPtherapy will not successfully terminate certain tachycardia episodes,and may in some cases result in an acceleration of the tachycardia,potentially worsening the tachycardia episode, and presenting a hazardto the patient.

In cases where ATP therapy is not successful in terminating atachycardia episode, or where ATP therapy results in an undesirableacceleration of the tachycardia, additional treatment may be warrantedor required. In such cases, one possible additional treatment involvesthe delivery of an anti-tachyarrhythmia shock, or a high voltage shock(HV shock), to terminate the tachycardia episode.

Some devices, such as IPD 16, do not also have the capability to delivera HV shock. So if ATP therapy be unsuccessful in treating thetachycardia episode, another device, such as ICD system 30, may berelied upon to deliver further treatment, which may include an HV shock.In such a system, ICD system 30 may serve as a backup device that mayprovide functionality not provided by a pacing device such as IPD 16.

However, in systems where ICD system 30 might not be present, or whereICD system 30 cannot be relied upon to deliver an HV shock, it may bebeneficial for IPD 16 to operate differently. For example, if IPD 16 isimplanted in a patient where no other device is available to deliver anHV shock, delivery of ATP therapy may not be appropriate, and may evenbe counterproductive. Accordingly, in a system where no device can berelied upon to deliver an HV shock, it may be appropriate for IPD 16 torefrain from initiating delivery of ATP therapy. Disabling delivery ofATP therapy, which may prevent delivery of ATP therapy to treat atachycardia episode, may in some cases be preferable to delivering ATPtherapy to treat a tachycardia episode.

FIG. 3 is a conceptual drawing illustrating example IPD 16 of FIG. 1that may include shock detection circuitry and/or utilize the shockdetection techniques of this disclosure. As shown in FIG. 3, IPD 16includes case 50, cap 58, electrode 60, electrode 52, fixationmechanisms 62, flange 54, and opening 56. Together, case 50 and cap 58may be considered the housing of IPD 16. In this manner, case 50 and cap58 may enclose and protect the various electrical components within IPD16. Case 50 may enclose substantially all of the electrical components,and cap 58 may seal case 50 and create the hermetically sealed housingof IPD 16. Although IPD 16 is generally described as including one ormore electrodes, IPD 16 may typically include at least two electrodes(e.g., electrodes 52 and 60) to deliver an electrical signal (e.g.,therapy such as ATP) and/or provide at least one sensing vector.

Electrodes 52 and 60 are carried on the housing created by case 50 andcap 58. In this manner, electrodes 52 and 60 may be considered leadlesselectrodes. In the example of FIG. 3, electrode 60 is disposed on theexterior surface of cap 58. Electrode 60 may be a circular electrodepositioned to contact cardiac tissue upon implantation. Electrode 52 maybe a ring or cylindrical electrode disposed on the exterior surface ofcase 50. Both case 50 and cap 58 may be electrically insulating.Electrode 60 may be used as a cathode and electrode 52 may be used as ananode, or vice versa, for delivering pacing stimulation therapy such asATP or post-shock pacing. However, electrodes 52 and 60 may be used inany stimulation configuration. In addition, electrodes 52 and 60 may beused to detect intrinsic electrical signals from cardiac muscle. Inother examples, IPD 16 may include three or more electrodes, where eachelectrode may deliver therapy and/or detect intrinsic signals. ATPdelivered by IPD 16, as compared with alternative devices, may beconsidered to be “painless” to patient 14 or even undetectable bypatient 14 since the electrical stimulation occurs very close to or atcardiac muscle and at relatively low energy levels.

Fixation mechanisms 62 may attach IPD 16 to cardiac tissue. Fixationmechanisms 62 may be active fixation tines, screws, clamps, adhesivemembers, or any other types of attaching a device to tissue. As shown inthe example of FIG. 3, fixation mechanisms 62 may be constructed of amemory material that retains a preformed shape. During implantation,fixation mechanisms 62 may be flexed forward to pierce tissue andallowed to flex back towards case 50. In this manner, fixationmechanisms 62 may be embedded within the target tissue.

Flange 54 may be provided on one end of case 50 to enable tethering orextraction of IPD 16. For example, a suture or other device may beinserted around flange 54 and/or through opening 56 and attached totissue. In this manner, flange 54 may provide a secondary attachmentstructure to tether or retain IPD 16 within heart 26 if fixationmechanisms 62 fail. Flange 54 and/or opening 56 may also be used toextract IPD 16 once the IPD needs to be explanted (or removed) frompatient 14 if such action is deemed necessary.

The techniques described herein are generally described with regard to aleadless pacing device or intracardiac pacing device such as IPD 16. IPD16 may be an example of an anti-tachycardia pacing device (ATPD).However, alternative implantable medical devices may be used to performthe same or similar functions as IPD 16 (e.g., delivering ATP to heart26) and communicate with ICD system 30. For example, an ATPD may includea small housing that carries an electrode, similar to IPD 16, andconfigured to be implanted within a chamber of heart 26. The ATPD mayalso include one or more relatively short leads configured to place oneor more respective additional electrodes at another location within thesame chamber of the heart or a different chamber of the heart. Thisconfiguration may be referred to as an Intercardiac Pacing Device. Inthis manner, the housing of the ATPD may not carry all of the electrodesused to deliver ATP or perform other functions. In other examples, eachelectrode of the ATPD may be carried by one or more leads (e.g., thehousing of the ATPD may not carry any of the electrodes).

In another example, the ATPD may be configured to be implanted externalto heart 26, e.g., near or attached to the epicardium of heart 26. Anelectrode carried by the housing of the ATPD may be placed in contactwith the epicardium and/or one or more electrodes of leads coupled tothe ATPD may be placed in contact with the epicardium at locationssufficient to provide therapy such as ATP (e.g., on external surfaces ofthe left and/or right ventricles). In some example, ICD system 30 maycommunicate with one or more leadless or leaded devices implantedinternal or external to heart 26.

FIG. 4 is a functional block diagram illustrating an exampleconfiguration of IPD 16 of FIG. 1. In the illustrated example, IPD 16includes a processing circuitry 90, memory 92, signal generationcircuitry 96, sensing circuitry 98, shock detection circuitry 99,activity sensor 100, communication circuitry 94, and power source 102.Memory 92 includes computer-readable instructions that, when executed byprocessing circuitry 90, cause IPD 16 and processing circuitry 90 toperform various functions attributed to IPD 16 and processing circuitry90 herein (e.g., detecting arrhythmias, communicating with ICD system30, and delivering anti-tachycardia pacing and post-shock pacing as wellas conventional brady pacing therapy). Memory 92 may include anyvolatile, non-volatile, magnetic, optical, or electrical media, such asa random access memory (RAM), read-only memory (ROM), non-volatile RAM(NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory,or any other digital or analog media.

Processing circuitry 90 may include any one or more of a microprocessor,a controller, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field-programmable gate array (FPGA), orequivalent discrete or analog logic circuitry. In some examples,processing circuitry 90 may include multiple components, such as anycombination of one or more microprocessors, one or more controllers, oneor more DSPs, one or more ASICs, or one or more FPGAs, as well as otherdiscrete or integrated logic circuitry. The functions attributed toprocessing circuitry 90 herein may be embodied as software, firmware,hardware or any combination thereof.

Processing circuitry 90 controls signal generation circuitry 96 todeliver stimulation therapy to heart 26 according to therapy parameters,which may be stored in memory 92. For example, processing circuitry 90may control signal generation circuitry 96 to deliver electrical pulseswith the amplitudes, pulse widths, frequency, or electrode polaritiesspecified by the therapy parameters. In this manner, signal generationcircuitry 96 may deliver pacing pulses (e.g., ATP pulses or post-shockpacing therapy, or conventional bradycardia pacing pulses) to heart 26via electrodes 52 and 60. Although IPD 16 may only include twoelectrodes, e.g., electrodes 52 and 60, IPD 16 may utilize three or moreelectrodes in other examples. IPD 16 may use any combination ofelectrodes to deliver therapy and/or detect electrical signals frompatient 14.

Signal generation circuitry 96 is electrically coupled to electrodes 52and 60 carried on the housing of IPD 16. In the illustrated example,signal generation circuitry 96 is configured to generate and deliverelectrical stimulation therapy to heart 26. For example, signalgeneration circuitry 96 may deliver the electrical stimulation therapyto a portion of cardiac muscle within heart 26 via electrodes 52 and 60.In some examples, signal generation circuitry 96 may deliver pacingstimulation, e.g., ATP therapy or post-shock pacing, in the form ofvoltage or current electrical pulses. In other examples, signalgeneration circuitry 96 may deliver one or more of these types ofstimulation in the form of other signals, such as sine waves, squarewaves, or other substantially continuous time signals. Although IPD 16is generally described as delivering pacing pulses, IPD 16 may delivercardioversion or defibrillation pulses in other examples.

ATP may be delivered to patient 14 as defined by a set of parameters,which may be stored in memory 92. These parameters may include pulseintervals, pulse width, current and/or voltage amplitudes, and durationsfor each pacing mode. For example, the pulse interval may be based on afraction of the detected ventricular tachycardia (VT) cycle length andbe between approximately 150 milliseconds and 500 milliseconds (e.g.,between approximately 2.0 hertz and 7.0 hertz), and the pulse width maybe between approximately 0.5 milliseconds and 2.0 milliseconds. Theamplitude of each pacing pulse may be between approximately 2.0 voltsand 10.0 volts. In some examples, the pulse amplitude may beapproximately 6.0 V and the pulse width may be approximately 1.5milliseconds; another example may include pulse amplitudes ofapproximately 5.0 V and pulse widths of approximately 1.0 milliseconds.Each train of pulses during ATP may last for a duration of betweenapproximately 0.5 seconds to approximately 15 seconds or be defined as aspecific number of pulses. Each pulse, or burst of pulses, may include aramp up in amplitude or in pulse rate. In addition, trains of pulses insuccessive ATP periods may be delivered at increasing pulse rate in anattempt to capture the heart and terminate the tachycardia. Example ATPparameters and other criteria involving the delivery of ATP aredescribed in U.S. Pat. No. 6,892,094 to Ousdigian et al., entitled,“COMBINED ANTI-TACHYCARDIA PACING (ATP) AND HIGH VOLTAGE THERAPY FORTREATING VENTRICULAR ARRHYTHMIAS,” and issued on May 10, 2005, theentire content of which is incorporated herein by reference.

Parameters that define post-shock pacing may also vary. In one example,monophasic post-shock pacing therapy may have a pulse width ofapproximately 1 millisecond at each phase and a pulse amplitude ofapproximately 5 volts. The pacing rate may be set to 30-60 beats perminute (0.5-1 hertz). The duration of each post-shock pacing session maybe between 10 seconds and 60 seconds, or even longer in other examples.In other examples, pulse widths, pulse amplitudes, and/or durations ofpost-shock pacing may be greater or lower.

Electrical sensing circuitry 98 monitors signals from electrodes 52 and60 in order to monitor electrical activity of heart 26, impedance, orother electrical phenomenon. Sensing may be done to determine heartrates or heart rate variability, or to detect arrhythmias (e.g.,tachyarrhythmias or bradycardia) or other electrical signals. Sensingcircuitry 98 may also include a switch module to select which of theavailable electrodes (or electrode polarity) are used to sense the heartactivity, depending upon which electrode combination, or electrodevector, is used in the current sensing configuration. In examples withseveral electrodes, processing circuitry 90 may select the electrodesthat function as sense electrodes, i.e., select the sensingconfiguration, via the switch module within sensing circuitry 98.Sensing circuitry 98 may include one or more detection channels, each ofwhich may be coupled to a selected electrode configuration for detectionof cardiac signals via that electrode configuration. Some detectionchannels may be configured to detect cardiac events, such as P- orR-waves, and provide indications of the occurrences of such events toprocessing circuitry 90, e.g., as described in U.S. Pat. No. 5,117,824to Keimel et al., which issued on Jun. 2, 1992 and is entitled,“APPARATUS FOR MONITORING ELECTRICAL PHYSIOLOGIC SIGNALS,” and isincorporated herein by reference in its entirety. Processing circuitry90 may control the functionality of sensing circuitry 98 by providingsignals via a data/address bus.

Processing circuitry 90 may include a timing and control module, whichmay be embodied as hardware, firmware, software, or any combinationthereof. The timing and control module may comprise a dedicated hardwarecircuit, such as an ASIC, separate from other processing circuitry 90components, such as a microprocessor, or a software module executed by acomponent of processing circuitry 90, which may be a microprocessor orASIC. The timing and control module may implement programmable counters.If IPD 16 is configured to generate and deliver pacing pulses to heart26, such counters may control the basic time intervals associated withDDD, VVI, DVI, VDD, AAI, DDI, DDDR, VVIR, DVIR, VDDR, AAIR, DDIR andother modes of pacing. Example IPDs that may deliver pacing using suchmodes are described in U.S. patent application Ser. No. 13/665,492 toBonner et al., entitled, “LEADLESS PACEMAKER SYSTEM,” and filed on Oct.31, 2012, or in U.S. patent application Ser. No. 13/665,601 to Bonner etal., entitled, “LEADLESS PACEMAKER SYSTEM,” and filed on Oct. 31, 2012.U.S. patent application Ser. No. 13/665,492 to Bonner et al. and U.S.patent Ser. No. 13/665,601 to Bonner et al. are both incorporated hereinby reference in their entireties.

Intervals defined by the timing and control module within processingcircuitry 90 may include atrial and ventricular pacing escape intervals,refractory periods during which sensed P-waves and R-waves areineffective to restart timing of the escape intervals, and the pulsewidths of the pacing pulses. As another example, the timing and controlmodule may withhold sensing from one or more channels of sensingcircuitry 98 for a time interval during and after delivery of electricalstimulation to heart 26. The durations of these intervals may bedetermined by processing circuitry 90 in response to stored data inmemory 92. The timing and control module of processing circuitry 90 mayalso determine the amplitude of the cardiac pacing pulses.

Interval counters implemented by the timing and control module ofprocessing circuitry 90 may be reset upon sensing of R-waves and P-waveswith detection channels of sensing circuitry 98. In examples in whichIPD 16 provides pacing, signal generation circuitry 96 may include paceroutput circuits that are coupled to electrodes 52 and 60, for example,appropriate for delivery of a bipolar or unipolar pacing pulse to one ofthe chambers of heart 26. In such examples, processing circuitry 90 mayreset the interval counters upon the generation of pacing pulses bysignal generation circuitry 96, and thereby control the basic timing ofcardiac pacing functions, including ATP or post-shock pacing.

The value of the count present in the interval counters when reset bysensed R-waves and P-waves may be used by processing circuitry 90 tomeasure the durations of R-R intervals, P-P intervals, P-R intervals andR-P intervals, which are measurements that may be stored in memory 92.Processing circuitry 90 may use the count in the interval counters todetect a tachyarrhythmia event, such as atrial fibrillation (AF), atrialtachycardia (AT), VF, or VT. These intervals may also be used to detectthe overall heart rate, ventricular contraction rate, and heart ratevariability. A portion of memory 92 may be configured as a plurality ofrecirculating buffers, capable of holding series of measured intervals,which may be analyzed by processing circuitry 90 in response to theoccurrence of a pace or sense interrupt to determine whether thepatient's heart 26 is presently exhibiting atrial or ventriculartachyarrhythmia.

In some examples, an arrhythmia detection method may include anysuitable tachyarrhythmia detection algorithms. In one example,processing circuitry 90 may utilize all or a subset of the rule-baseddetection methods described in U.S. Pat. No. 5,545,186 to Olson et al.,entitled, “PRIORITIZED RULE BASED METHOD AND APPARATUS FOR DIAGNOSIS ANDTREATMENT OF ARRHYTHMIAS,” which issued on Aug. 13, 1996, or in U.S.Pat. No. 5,755,736 to Gillberg et al., entitled, “PRIORITIZED RULE BASEDMETHOD AND APPARATUS FOR DIAGNOSIS AND TREATMENT OF ARRHYTHMIAS,” whichissued on May 26, 1998. U.S. Pat. No. 5,545,186 to Olson et al. U.S.Pat. No. 5,755,736 to Gillberg et al. is incorporated herein byreference in their entireties. However, other arrhythmia detectionmethodologies, such as those methodologies that utilize timing andmorphology of the electrocardiogram, may also be employed by processingcircuitry 90 in other examples.

In some examples, processing circuitry 90 may determine thattachyarrhythmia has occurred by identification of shortened R-R (or P-P)interval lengths. Generally, processing circuitry 90 detects tachycardiawhen the interval length falls below 220 milliseconds and fibrillationwhen the interval length falls below 180 milliseconds. In otherexamples, processing circuitry 70 may detect ventricular tachycardiawhen the interval length falls between 330 milliseconds and ventricularfibrillation when the interval length falls below 240 milliseconds.These interval lengths are merely examples, and a user may define theinterval lengths as desired, which may then be stored within memory 92.This interval length may need to be detected for a certain number ofconsecutive cycles, for a certain percentage of cycles within a runningwindow, or a running average for a certain number of cardiac cycles, asexamples. In other examples, additional physiological parameters may beused to detect an arrhythmia. For example, processing circuitry 90 mayanalyze one or more morphology measurements, impedances, or any otherphysiological measurements to determine that patient 14 is experiencinga tachyarrhythmia.

In the event that an ATP regimen is desired, timing intervals forcontrolling the generation of ATP therapies by signal generationcircuitry 96 may be loaded by processing circuitry 90 into the timingand control module to control the operation of the escape intervalcounters therein and to define refractory periods during which detectionof R-waves and P-waves is ineffective to restart the escape intervalcounters for the ATP. An ATP regimen may be desired if processingcircuitry 90 detects an atrial or ventricular tachyarrhythmia based onsignals from sensing circuitry 98, and/or receives a command fromanother device or system, such as ICD system 30, as examples.

In addition to detecting and identifying specific types of cardiacrhythms, sensing circuitry 98 may also sample the detected intrinsicsignals to generate an electrogram or other time-based indication ofcardiac events. Processing circuitry 90 may also be able to coordinatethe delivery of pacing pulses from different IPDs implanted in differentchambers of heart 26, such as an IPD implanted in atrium and/or an IPDimplanted in left ventricle. For example, processing circuitry 90 mayidentify delivered pulses from other IPDs via sensing circuitry 98 andupdate pulse timing to accomplish a selected pacing regimen. Thisdetection may be on a pulse-to-pulse or beat-to-beat basis, or on a lessfrequent basis to make slight modifications to pulse rate over time. Inother examples, IPDs may communicate with each other via communicationcircuitry 94 and/or instructions over a carrier wave (such as astimulation waveform). In this manner, ATP or post-shock pacing may becoordinated from multiple IPDs.

Shock detection circuitry 99 may be used to detect anti-tachyarrhythmiashocks delivered by ICD system 30 or another device. For example,processing circuitry 90 may enable shock detection circuitry 99 inresponse to detecting a tachyarrhythmia or receiving a communicationindicating that an arrhythmia has been detected or a shock is imminent.Processing circuitry 90 may also disable shock detection circuitry 99after a predetermined time period has elapsed or when a shock isotherwise not (or no longer) anticipated. When shock detection circuitry99 is enabled, shock detection circuitry 99 may identify when anelectrical signal received by sensing circuitry 98 is representative ofa cardioversion or defibrillation pulse.

In response to detecting a shock via shock detection circuitry 99,processing circuitry 90 may begin post-shock pacing when suchfunctionality has been enabled for therapy. Processing circuitry 90 mayalso re-start post-shock pacing in response to detecting additionalshocks via shock detection circuitry 99. In some examples, processingcircuitry 90 may terminate ATP upon detection of a shock.

Shock detection circuitry 99 may detect an anti-tachyarrhythmia shock,e.g., a defibrillation or cardioversion pulse, delivered by ICD system30 or an external defibrillator based on the detection of an electricalsignal across two or more electrodes. In order to detect theanti-tachyarrhythmia shock, shock detection circuitry 99 may detect oneor more signal characteristics of an anti-tachyarrhythmia shockincluding: detection of the high amplitude level of ananti-tachyarrhythmia shock, detection of a high slew rate of the leadingand trailing edges, and detection of a large post-shock polarizationchange. Detection of more than one signal characteristic may improvesensitivity and/or specificity of the shock anti-tachyarrhythmia shockdetection. For example, shock detection circuitry 99 may detect a highlevel of an anti-tachyarrhythmia shock in combination with one or bothof the detection of a high slew rate of the leading and trailing edgesand/or the detection of a large post-shock polarization change. Exampleshock detection circuitry is described in U.S. Pat. No. 9,278,229 toReinke et al., entitled “Anti-tachyarrhythmia shock detection,” whichissued on Mar. 8, 2016, is hereby incorporated by reference.

Although illustrated separately in the example of FIG. 4, shockdetection circuitry 99 may, in some examples, be included as part ofprocessing circuitry 90. In some examples, the shock detectionfunctionality attributed to shock detection circuitry 99 may be afunctional module executed by processing circuitry 90.

Memory 92 may be configured to store a variety of operationalparameters, therapy parameters, sensed and detected data, and any otherinformation related to the therapy and treatment of patient 14. In theexample of FIG. 4, memory 92 may store sensed ECGs, detectedarrhythmias, communications from ICD system 30, and therapy parametersthat define ATP and/or post-shock pacing regimens. In other examples,memory 92 may act as a temporary buffer for storing data until it can beuploaded to ICD system 30, another implanted device, or device 21.

Activity sensor 100 may be contained within the housing of IPD 16 andinclude one or more accelerometers or other devices capable of detectingmotion and/or position of IPD 16. For example, activity sensor 100 mayinclude a 3-axis accelerometer that is configured to detectaccelerations in any direction in space. Specifically, the 3-axisaccelerator may be used to detect IPD 16 motion that may be indicativeof cardiac events and/or noise. For example, processing circuitry 90 maymonitor the accelerations from activity sensor 100 to confirm or detectarrhythmias. Since IPD 16 may move with a chamber wall of heart 26, thedetected changes in acceleration may also be indicative of contractions.Therefore, IPD 16 may be configured to identify heart rates and confirmarrhythmias, such as a tachycardia, sensed via sensing circuitry 98.

Communication circuitry 94 includes any suitable hardware, firmware,software or any combination thereof for communicating with anotherdevice, such as device 21 or ICD system 30 (FIG. 1). Under the controlof processing circuitry 90, communication circuitry 94 may receivedownlink telemetry from and send uplink telemetry to device 21 with theaid of an antenna, which may be internal and/or external. Processingcircuitry 90 may provide the data to be uplinked to device 21 and thecontrol signals for the telemetry circuit within communication circuitry94, e.g., via an address/data bus. In some examples, communicationcircuitry 94 may provide received data to processing circuitry 90 via amultiplexer.

In some examples, IPD 16 may signal device 21 to further communicatewith and pass the alert through a network such as the MedtronicCareLink® Network developed by Medtronic, Inc., of Minneapolis, Minn.,or some other network linking patient 14 to a clinician. IPD 16 mayspontaneously transmit information to the network or in response to aninterrogation request from a user.

Power source 102 may be any type of device that is configured to hold acharge to operate the circuitry of IPD 16. Power source 102 may beprovided as a rechargeable or non-rechargeable battery. In otherexamples, power source 102 may incorporate an energy scavenging systemthat stores electrical energy from movement of IPD 16 within patient 14.

Processing circuitry 90 may detect an enable event as a result ofinitialization of IPD 16 or as a result of a power-on cycle. In otherexamples, processing circuitry 90 may detect an enable event based oninput from sensing circuitry 98, signal generation circuitry 96, shockdetection circuitry 99, or activity sensor 100. In other examples, anenable event may be detected based on logic within processing circuitry90 or based on processing circuitry 90 executing instructions stored inmemory 92. In still further examples, communication circuitry 94 withinIPD 16 may detect input or a signal from another device operated by aclinician, and may output an indication of an enable event to processingcircuitry 90, which may determine, based on the indication of the enableevent, that an enable event has been received.

Processing circuitry 90 may operate to control signal generationcircuitry 96 when enabling or disabling ATP therapy. Processingcircuitry 90 within IPD 16 may enable delivery of anti-tachyarrhythmiapacing (ATP) therapy (504) by outputting to signal generation circuitry96 information that causes signal generation circuitry 96 to enabledelivery of ATP, or in other examples, processing circuitry 90 maycontrol signal generation circuitry 96 in a way that results in enablingdelivery of ATP. Disabling delivery of ATP may include processingcircuitry 90 outputting to signal generation circuitry 96 informationthat causes signal generation circuitry 96 to disable delivery of ATP,or in other examples, may include processing circuitry 90 controllingsignal generation circuitry 96 in such a way that results in disablingdelivery of ATP.

FIG. 5 is a functional block diagram illustrating an exampleconfiguration of ICD system 30 of FIG. 1. As described in connectionwith FIG. 1, ICD system 30 includes ICD 9 connected to at least oneimplantable cardiac defibrillation lead 25. As shown in FIG. 5, ICDsystem 30 includes a processing circuitry 70, memory 72, shock circuitry75, signal generation circuitry 76, sensing circuitry 78, communicationcircuitry 80, activity sensor 82, and power source 84. Memory 72includes computer-readable instructions that, when executed byprocessing circuitry 70, cause ICD system 30 and processing circuitry 70to perform various functions attributed to ICD system 30 and processingcircuitry 70 herein (e.g., detection of tachyarrhythmias, communicationwith IPD 16, and/or delivery of anti-tachyarrhythmia shock therapy).Memory 72 may include any volatile, non-volatile, magnetic, optical, orelectrical media, such as a random access memory (RAM), read-only memory(ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM(EEPROM), flash memory, or any other digital or analog media.

Processing circuitry 70 may include any one or more of a microprocessor,a controller, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field-programmable gate array (FPGA), orequivalent discrete or analog logic circuitry. In some examples,processing circuitry 70 may include multiple components, such as anycombination of one or more microprocessors, one or more controllers, oneor more DSPs, one or more ASICs, or one or more FPGAs, as well as otherdiscrete or integrated logic circuitry. The functions attributed toprocessing circuitry 70 herein may be embodied as software, firmware,hardware or any combination thereof.

Processing circuitry 70 controls signal generation circuitry 76 todeliver stimulation therapy to heart 26 according to therapy parameters,which may be stored in memory 72. For example, processing circuitry 70may control signal generation circuitry 76 to deliver electrical pulses(e.g., shock pulses) with the amplitudes, pulse widths, frequency, orelectrode polarities specified by the therapy parameters. In thismanner, signal generation circuitry 76 may deliver electrical pulses toheart 26 via electrodes 28 (or 28 a or 28 b) and the conductive housingelectrode 31 of ICD 9. In addition, via any combination of electrodes,28, 32 a, 32 b and/or housing 31 may be connected to sensing circuitry78. In further examples, signal generation circuitry 76 may deliverelectrical pulses to heart 26 via any combination of electrodes, 28, 32a, 32 b and/or housing 31, although electrodes 32 a and 32 b, may morefrequently be used for sensing. ICD system 30 may use any combination ofelectrodes to deliver anti-tachycardia therapy and/or detect electricalsignals from patient 14. However, in general, coil electrode 28 andhousing 31 may be used to deliver an anti-tachyarrhythmia shock.

Signal generation circuitry 76 may also include shock circuitry 75.Shock circuitry 75 may include circuitry and/or capacitors required todeliver an anti-tachyarrhythmia shock. For example, signal generationcircuitry 76 may charge shock circuitry 75 to prepare for delivering ashock. Shock circuitry 75 may then discharge to enable signal generationcircuitry 76 to deliver the shock to patient 14 via one or moreelectrodes. In other examples, shock circuitry 75 may be located withinICD system 30 but outside of signal generation circuitry 76.

Signal generation circuitry 76 is electrically coupled to electrodes 28,32 a, and 32 b. In the illustrated example, signal generation circuitry76 is configured to generate and deliver electrical anti-tachyarrhythmiashock therapy to heart 26. For example, signal generation circuitry 76may, using shock circuitry 75, deliver shocks to heart 26 via a subsetof electrodes 28, 32 a, and 32 b. In some examples, signal generationcircuitry 76 may deliver pacing stimulation (e.g., post-shock pacing),and cardioversion or defibrillation pulses in the form of voltage orcurrent electrical pulses. In other examples, signal generationcircuitry 76 may deliver one or more of these types of stimulation orshocks in voltage or current in the form of other signals, such as sinewaves, square waves, or other substantially continuous time signals.

Signal generation circuitry 76 may include a switch module andprocessing circuitry 70 may use the switch module to select, e.g., via adata/address bus, which of the available electrodes are used to delivershock and/or pacing pulses. The switch module may include a switcharray, switch matrix, multiplexer, or any other type of switching devicesuitable to selectively couple stimulation energy to selectedelectrodes.

Electrical sensing circuitry 78 may be configured to monitor signalsfrom at least two of the electrodes 28, 32 a, 32 b and housing 31 inorder to monitor electrical activity of heart 26, impedance, or otherelectrical phenomenon. Sensing may be done to determine heart rates orheart rate variability, or to detect arrhythmias (e.g., tachyarrhythmia)or other electrical signals. Sensing circuitry 78 may also include aswitch module to select which of the available electrodes are used tosense the heart activity, depending upon which electrode combination, orelectrode vector, is used in the current sensing configuration. Inexamples with several electrodes, processing circuitry 70 may select theelectrodes that function as sense electrodes, i.e., select the sensingconfiguration, via the switch module within sensing module 78. Sensingmodule 78 may include one or more detection channels, each of which maybe coupled to a selected electrode configuration for detection ofcardiac signals via that electrode configuration. Some detectionchannels may be configured to detect cardiac events, such as P- orR-waves, and provide indications of the occurrences of such events toprocessing circuitry 70, e.g., as described in U.S. Pat. No. 5,117,824to Keimel et al., which issued on Jun. 2, 1992 and is entitled,“APPARATUS FOR MONITORING ELECTRICAL PHYSIOLOGIC SIGNALS,” and isincorporated herein by reference in its entirety. Processing circuitry70 may control the functionality of sensing module 78 by providingsignals via a data/address bus.

Processing circuitry 70 may include a timing and control module, whichmay be embodied as hardware, firmware, software, or any combinationthereof. The timing and control module may comprise a dedicated hardwarecircuit, such as an ASIC, separate from other processing circuitry 70components, such as a microprocessor, or a software module executed by acomponent of processing circuitry 70, which may be a microprocessor orASIC. The timing and control module may implement programmable counters.If ICD system 30 is configured to generate and deliver pacing pulses toheart 26, such counters may control the basic time intervals associatedwith DDD, VVI, DVI, VDD, AAI, DDI, DDDR, VVIR, DVIR, VDDR, AAIR, DDIRand other modes of pacing.

Intervals defined by the timing and control module within processingcircuitry 70 may include atrial and ventricular pacing escape intervals,refractory periods during which sensed P-waves and R-waves areineffective to restart timing of the escape intervals, and the pulsewidths of the pacing pulses. As another example, the timing and controlmodule may withhold sensing from one or more channels of sensingcircuitry 78 for a time interval during and after delivery of electricalstimulation to heart 26. The durations of these intervals may bedetermined by processing circuitry 70 in response to stored data inmemory 72. The timing and control module of processing circuitry 70 mayalso determine the amplitude of the cardiac pacing pulses.

Interval counters implemented by the timing and control module ofprocessing circuitry 70 may be reset upon sensing of R-waves and P-waveswith detection channels of sensing circuitry 78. The value of the countpresent in the interval counters when reset by sensed R-waves andP-waves may be used by processing circuitry 70 to measure the durationsof R-R intervals, P-P intervals, P-R intervals and R-P intervals, whichare measurements that may be stored in memory 72. Processing circuitry70 may use the count in the interval counters to detect atachyarrhythmia event, such as AF, AT, VF, or VT. These intervals mayalso be used to detect the overall heart rate, ventricular contractionrate, and heart rate variability. A portion of memory 72 may beconfigured as a plurality of recirculating buffers, capable of holdingseries of measured intervals, which may be analyzed by processingcircuitry 70 in response to the occurrence of a pace or sense interruptto determine whether the patient's heart 26 is presently exhibitingatrial or ventricular tachyarrhythmia.

In some examples, an arrhythmia detection method may include anysuitable tachyarrhythmia detection algorithms. In one example,processing circuitry 70 may utilize all or a subset of the rule-baseddetection methods described in U.S. Pat. No. 5,545,186 to Olson et al.,entitled, “PRIORITIZED RULE BASED METHOD AND APPARATUS FOR DIAGNOSIS ANDTREATMENT OF ARRHYTHMIAS,” which issued on Aug. 13, 1996, or in U.S.Pat. No. 5,755,736 to Gillberg et al., entitled, “PRIORITIZED RULE BASEDMETHOD AND APPARATUS FOR DIAGNOSIS AND TREATMENT OF ARRHYTHMIAS,” whichissued on May 26, 1998. U.S. Pat. No. 5,545,186 to Olson et al. U.S.Pat. No. 5,755,736 to Gillberg et al. is incorporated herein byreference in their entireties. However, other arrhythmia detectionmethodologies, such as those methodologies that utilize timing andmorphology of the electrocardiogram, may also be employed by processingcircuitry 70 in other examples.

In some examples, processing circuitry 70 may determine thattachyarrhythmia has occurred by identification of shortened R-R (or P-P)interval lengths. Generally, processing circuitry 70 detects tachycardiawhen the interval length falls below 220 milliseconds and fibrillationwhen the interval length falls below 180 milliseconds. In otherexamples, processing circuitry 70 may detect ventricular tachycardiawhen the interval length falls between 330 milliseconds and ventricularfibrillation when the interval length falls between 240 milliseconds.These interval lengths are merely examples, and a user may define theinterval lengths as desired, which may then be stored within memory 72.This interval length may need to be detected for a certain number ofconsecutive cycles, for a certain percentage of cycles within a runningwindow, or a running average for a certain number of cardiac cycles, asexamples.

In the event that processing circuitry 70 detects an atrial orventricular tachyarrhythmia based on signals from sensing circuitry 78,and an anti-tachyarrhythmia pacing regimen is desired, timing intervalsfor controlling the generation of anti-tachyarrhythmia pacing therapiesby signal generation circuitry 76 may be loaded by processing circuitry70 into the timing and control module to control the operation of theescape interval counters therein and to define refractory periods duringwhich detection of R-waves and P-waves is ineffective to restart theescape interval counters for the an anti-tachyarrhythmia pacing. Inaddition to detecting and identifying specific types of cardiac rhythms,sensing circuitry 78 may also sample the detected intrinsic signals togenerate an electrogram or other time-based indication of cardiacevents.

In some examples, communication circuitry 80 may be used to detectcommunication signals from IPD 16. Instead, IPD 16 may generateelectrical signals via one or more electrodes with amplitudes and/orpatterns representative of information to be sent to ICD system 30. Theelectrical signals may be carried by pacing pulses or separatecommunication signals configured to be detected by ICD system 30. Inthis manner, communication circuitry 80 may be configured to monitorsignals sensed by sensing circuitry 78 and determine when acommunication message is received from IPD 16.

In other examples, ICD system 30 may also transmit communicationmessages to IPD 16 using electrical signals transmitted from one or moreof electrodes 28, 32 a, 32 b and housing 31. In this case, communicationcircuitry 80 may be coupled to signal generation circuitry 76 to controlthe parameters of generated electrical signals or pulses. Alternatively,processing circuitry 70 may detect communications via sensing circuitry78 and/or generate communications for deliver via signal generationcircuitry 76. Although communication circuitry 80 may be used tocommunicate using electrical signals via electrodes 28, 32 a, 32 b andhousing 31, communication circuitry 80 may alternatively or in additionuse wireless protocols, such as RF telemetry, inductive telemetry,acoustics, or TCC to communicate with IPD 16 or other medical devices.In some examples, communication circuitry 80 may include this wirelesscommunication functionality.

Communication circuitry 80 includes any suitable hardware, firmware,software or any combination thereof for communicating with anotherdevice, such as device 21 (FIG. 1). Communication circuitry 80 maytransmit generated or received arrhythmia data, therapy parametervalues, communications between ICD system 30 and IPD 16, or any otherinformation. For example, communication circuitry 80 may transmitinformation representative of sensed physiological data such as R-Rintervals or any other data that may be used by IPD 16 to determine acondition of patient 14. Communication circuitry 80 may also be used toreceive updated therapy parameters from device 21. Under the control ofprocessing circuitry 70, communication circuitry 80 may receive downlinktelemetry from and send uplink telemetry to device 21 with the aid of anantenna, which may be internal and/or external. Processing circuitry 70may provide the data to be uplinked to device 21 and the control signalsfor the telemetry circuit within communication circuitry 80, e.g., viaan address/data bus. In some examples, communication circuitry 80 mayprovide received data to processing circuitry 70 via a multiplexer.

Memory 72 may be configured to store a variety of operationalparameters, therapy parameters, sensed and detected data, and any otherinformation related to the monitoring, therapy and treatment of patient14. Memory 72 may store, for example, thresholds and parametersindicative of tachyarrhythmias and/or therapy parameter values that atleast partially define delivered anti-tachyarrhythmia shocks. In someexamples, memory 72 may also store communications transmitted to and/orreceived from IPD 16.

Activity sensor 82 may be contained within the housing of ICD system 30and include one or more accelerometers or other devices capable ofdetecting motion and/or position of ICD system 30. For example, activitysensor 82 may include a 3-axis accelerometer that is configured todetect accelerations in any direction in space. Accelerations detectedby activity sensor 82 may be used by processing circuitry 70 to identifypotential noise in signals detected by sensing circuitry 78 and/orconfirm the detection of arrhythmias or other patient conditions.

In some examples, ICD system 30 may signal device 21 to furthercommunicate with and pass the alert through a network such as theMedtronic CareLink® Network developed by Medtronic, Inc., ofMinneapolis, Minn., or some other network linking patient 14 to aclinician. ICD system 30 may spontaneously transmit the diagnosticinformation to the network or in response to an interrogation requestfrom a user.

Power source 84 may be any type of device that is configured to hold acharge to operate the circuitry of ICD system 30. Power source 84 may beprovided as a rechargeable or non-rechargeable battery. In otherexamples, power source 84 may also incorporate an energy scavengingsystem that stores electrical energy from movement of ICD system 30within patient 14.

Some ICD systems, such as ICD system 30 in FIG. 5, may have limitedcapabilities to deliver anti-tachycardia pacing and post-shock pacing aswell as conventional brady pacing therapy. In some examples, anotherdevice, such as IPD 16 (shown in FIG. 4), may be used to deliver suchpacing therapies. In particular, delivery of anti-tachycardia pacing(ATP) therapy by a device such as IPD 16 may be helpful in treatingtachycardia episodes. However, when using ATP therapy to treat atachycardia episode, there is a risk that the delivery of ATP therapywill not successfully terminate certain tachycardia episodes. Further,delivery of ATP therapy may in some cases result in an acceleration ofthe tachycardia, potentially worsening the tachycardia episode, andpresenting a hazard to the patient.

In cases where ATP therapy is not successful in terminating atachycardia episode, or where ATP therapy results in an undesirableacceleration of the tachycardia, additional treatment may be warrantedor required. In such cases, one possible additional treatment involvesthe delivery of an anti-tachyarrhythmia shock, or a high voltage shock(HV shock), to terminate the tachycardia episode. Accordingly, in someexamples, treatment of a tachycardia episode may initially includedelivery of ATP therapy. And in some cases where ATP therapy is notsuccessful in terminating a tachycardia episode, treatment may includeadditional therapy, such as the delivery of an HV shock.

Some devices that are configured to deliver ATP therapy, such as IPD 16,do not also have the capability to deliver a HV shock. In an examplewhere IPD 16 may not have the ability to deliver an HV shock, IPD 16 maynevertheless deliver ATP therapy to treat tachycardia episodes. ShouldATP therapy be unsuccessful in treating the tachycardia episode, anotherdevice, such as ICD system 30 (shown in FIG. 5), may be relied upon todeliver further treatment, which may include an HV shock. In such asystem, ICD system 30 may serve as a backup device that may providefunctionality not provided by a pacing device such as IPD 16.

However, in systems where ICD system 30 might not be present, or whereICD system 30 cannot be relied upon to deliver an HV shock, it may beappropriate for IPD 16 to operate differently. For example, if IPD 16 isimplanted in a patient where there is no ICD system 30 and no otherdevice is available to deliver an HV shock, delivery of ATP therapy maynot be appropriate, and may even be counterproductive, since in somecases, delivery of ATP therapy may lead to an acceleration of thetachycardia. Further, in situations where both IPD 16 and anotherdevice, such as ICD system 30, are implanted in a patient as shown inFIG. 1, it is possible that ICD system 30 cannot be relied upon todeliver an HV shock. Such situations may include instances where ICDsystem 30 may not be operating properly, may be nearing the end of itsuseful life, or may have limited remaining battery power. Accordingly,in a system where no device can be relied upon to deliver an HV shock,it may be appropriate for IPD 16 to refrain from initiating delivery ofATP therapy. Disabling delivery of ATP therapy, which may preventdelivery of ATP therapy to treat a tachycardia episode, may in somecases be preferable to delivering ATP therapy to treat a tachycardiaepisode.

FIG. 6 is a functional block diagram of an example configuration ofexternal device 21. In the example of FIG. 6, external device 21includes processing circuitry 140, memory 142, user interface (UI) 144,and telemetry circuitry 146. External device 21 may be a dedicatedhardware device with dedicated software for the programming and/orinterrogation of one or more devices within cardiac system 8, includingeither IPD 16 or IMD 30. Alternatively, external device 21 may be anoff-the-shelf computing device, e.g., running an application thatenables external device 21 to program and/or interrogate devices withincardiac system 8.

In some examples, a clinician or user uses external device 21 to selector program values for operational parameters of devices within cardiacsystem 8, e.g., for cardiac sensing, therapy delivery, and disablingand/or enabling IPD 16. In some examples, a clinician uses externaldevice 21 to receive data collected by devices within system 8, such asinformation about the condition of ICD system 30, including informationrelating to remaining battery life. External device 21 may also receivedata from IPD 16, including whether it delivery of ATP is currentlyenabled or not. External device 21 may also receive other operationaland performance data of devices within cardiac system 8.

The user may interact with external device 21 via UI 144, which mayinclude a display to present a graphical user interface to a user, and akeypad or another mechanism for receiving input from a user. Externaldevice 21 may communicate wirelessly with one or more devices withinsystem 8 using telemetry circuitry 146, which may be configured for RFcommunication with communication circuitry 94 of IPD 16 or communicationcircuitry 80 of ICD 30. Any appropriate communication protocols beyondRF communication may be used.

Processing circuitry 140 may include any combination of integratedcircuitry, discrete logic circuitry, analog circuitry, such as one ormore microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), or field-programmable gate arrays(FPGAs). In some examples, processing circuitry 106 may include multiplecomponents, such as any combination of one or more microprocessors, oneor more DSPs, one or more ASICs, or one or more FPGAs, as well as otherdiscrete or integrated logic circuitry, and/or analog circuitry.

Memory 142 may store program instructions, which may include one or moreprogram modules, which are executable by processing circuitry 140. Whenexecuted by processing circuitry 140, such program instructions maycause processing circuitry 140 and external device 21 to provide thefunctionality ascribed to them herein. The program instructions may beembodied in software, firmware and/or RAMware. Memory 142 may includeany volatile, non-volatile, magnetic, optical, or electrical media, suchas a random access memory (RAM), read-only memory (ROM), non-volatileRAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flashmemory, or any other digital media.

A clinician may use external device 21 in FIG. 6 to communicate with IPD16, and thereby enable or disable delivery of ATP therapy in accordancewith one or more aspects of the present disclosure. As described below,a clinician may also perform an assessment of devices within cardiacsystem 8 and use external device 21 to modify or update parametersstored within IPD 16 or other devices within cardiac system 8.

FIG. 7 is a functional block diagram illustrating an example system thatincludes external computing devices, such as a server 164 and one ormore other computing devices 170A-170N, that are coupled to deviceswithin cardiac system 8 (including IPD 16 and ICD system 30) andexternal device 21 via a network 162. In this example, IPD16 may usecommunication circuitry 94 to, e.g., at different times and/or indifferent locations or settings, communicate with external device 21 viaa first wireless connection, and to communicate with an access point 160via a second wireless connection. Similarly, ICD system 30 may usecommunication circuitry 80 to, e.g., at different times and/or indifferent locations or settings, communicate with external device 21 viaa first wireless connection, and to communicate with an access point 160via a second wireless connection. In the example of FIG. 7, access point160, external device 21, server 164, and computing devices 170A-170N areinterconnected, and able to communicate with each other, through network162.

Access point 160 may comprise a device that connects to network 162 viaany of a variety of connections, such as telephone dial-up, digitalsubscriber line (DSL), or cable modem connections. In other examples,access point 160 may be coupled to network 162 through different formsof connections, including wired or wireless connections. In someexamples, access point 160 may be co-located with patient 14. Accesspoint 160 may interrogate devices within the cardiac system 8, e.g.,periodically or in response to a command from patient 14 or network 162,to retrieve information such as operational data from devices withincardiac system 8. Access point 160 may provide the retrieved data toserver 164 via network 162. In accordance with one or more aspects ofthe present disclosure, a clinician may use external device 21 in FIG. 7to communicate with IPD 16, and thereby enable or disable delivery ofATP therapy, and in some examples, modify or update parameters storedwithin IPD 16 or other devices within cardiac system 8

In some cases, server 164 may be configured to provide a secure storagesite for data that has been collected from one or more devices withincardiac system 8 and/or external device 21, such as the Internet. Insome cases, server 164 may assemble data in web pages or other documentsfor viewing by trained professionals, such as clinicians, via computingdevices 170A-170N. The illustrated system of FIG. 7 may be implemented,in some aspects, with general network technology and functionalitysimilar to that provided by the Medtronic CareLink® Network developed byMedtronic plc, of Dublin, Ireland.

FIG. 8 is a flow diagram illustrating an example process of a system inaccordance with one or more aspects of the present disclosure. Forpurposes of illustration, FIG. 8 is described below within the contextof operations performed by IPD 16 of FIG. 1 and FIG. 4, but theoperations illustrated by the example of FIG. 8 may be performed by anymedical device configured to deliver ATP. FIG. 8 illustrates an exampleprocess for enabling and disabling delivery of ATP therapy in an exampleIPD 16. In the example described in connection with FIG. 8, the exampleIPD 16 may have capabilities for delivering ATP therapy, but might nothave capabilities for delivering an anti-tachyarrhythmia shock (HVshock).

In FIG. 8, processing circuitry 90 within IPD 16 may detect an enableevent (502). IPD 16 may detect an enable event as a result ofinitialization of IPD 16 or as a result of a power-on cycle. Forinstance, processing circuitry 90 may detect an enable event occurringwhen power is supplied to IPD 16, which may happen before, during, orafter IPD 16 is implanted in patient 14. In other examples, processingcircuitry 90 may detect an enable event based on input from sensingcircuitry 98, signal generation circuitry 96, shock detection circuitry99, or activity sensor 100. In other examples, an enable event may bedetected based on logic within processing circuitry 90 or based onprocessing circuitry 90 executing instructions stored in memory 92.

In still further examples, communication circuitry 94 within IPD 16 maydetect input or a signal from another device, and may output anindication of an enable event to processing circuitry 90, which maydetermine, based on the indication of the enable event, that an enableevent has been received. In such examples, the signal may originate froman internal device or an external device that may transmit the signalthrough wireless telemetry or through any appropriate communicationtechnique. In some examples, the signal may originate from an internaldevice, such as ICD system 30. In other examples, the signal may alsooriginate from an external device, such as external device 21 operatedby a clinician or another person, which may include patient 14. In stillfurther examples, the signal may also originate from external device 21automatically or from another device configured to determine appropriatecircumstances for sending an enable signal to IPD 16.

Responsive to detecting an enable event, processing circuitry 90 withinIPD 16 may enable delivery of anti-tachyarrhythmia pacing (ATP) therapy(504), which may thereafter result in IPD 16 delivering pacing signalsto heart 26 when ATP therapy may be considered appropriate. To cause ATPtherapies to be enabled, processing circuitry 90 may in some examplesoutput to signal generation circuitry 96 information that causes signalgeneration circuitry 96 to enable delivery of ATP, or in other examples,processing circuitry 90 may control signal generation circuitry 96 in away that results in enabling delivery of ATP. In accordance with one ormore aspects of the present disclosure, enabling delivery of ATP mayallow ATP therapy to be delivered during a tachycardia episode.

After enabling delivery of ATP therapy, IPD 16 may determine whether itis appropriate for delivery of ATP to continue to be enabled (506). Asdescribed above, it may be appropriate for IPD 16 to refrain from ordisable delivery of ATP therapy in some cases, such as when no device isconsidered available to deliver an HV shock. In accordance with one ormore aspects of the present disclosure, IPD 16 may determine whether todisable ATP by evaluating whether another device may be available todeliver an HV shock. To perform this evaluation, processing circuitry 90within IPD 16 may execute instructions stored on memory 92 and mayprocess available information relevant to such an evaluation, which mayinclude information relating to the capabilities and availability ofdevices in cardiac system 8. Such available information may be derivedfrom communication circuitry 94 detecting direct or broadcastcommunications that may originate from devices within cardiac system 8.Such available information may also include information derived fromcommunication circuitry 94 detecting direct or broadcast communicationsthat may originate from external devices (e.g., devices not included incardiac system 8). Such external devices may include external device 21,which may be operated by a clinician or by patient 14 to transmit asignal communicating information to IPD 16. In still other examples,available information may include information received by processingcircuitry 90 from signal generation circuitry 96, sensing circuitry 98,shock detection circuitry 99, or activity sensor 100, and may furtherinclude information stored in memory 92.

In some examples, as long as IPD 16, or processing circuitry 90 withinIPD 16, determines that a device capable of delivering an HV shock canbe considered available, delivery of ATP may remain enabled. However,responsive to a determination made by IPD 16 (or processing circuitry 90within IPD 16) that no HV backup device can be considered available (NOpath from 506), IPD 16 may, in some examples, disable delivery of ATP(508). Disabling delivery of ATP may include processing circuitry 90outputting to signal generation circuitry 96 information that causessignal generation circuitry 96 to disable delivery of ATP, or in otherexamples, may include processing circuitry 90 controlling signalgeneration circuitry 96 in such a way that results in disabling deliveryof ATP. In accordance with one or more aspects of the presentdisclosure, disabling ATP may prevent delivery of ATP when an HV backupdevice is not available.

The determination made at 506 (within sub-process 520), which in someexamples may include assessing whether an HV backup device can beconsidered available, may not always be accurate. In some examples,which may include when IPD 16 and ICD system 30 may be operatingindependently and might not be in communication with each other, IPD 16might not be able to make an accurate determination (or a determinationhaving a high degree of certainty), whether ICD system 30 is availableas an HV backup device. For example, in some situations, IPD 16 maydetermine at 506 that an HV backup device is not considered available todeliver an HV shock, when in reality, one or more HV backup devices mayin fact be available to deliver an HV shock if appropriate. When thisinaccurate assessment is made, delivery of ATP may be disabled, eventhough an HV backup device is available to deliver an HV shock.Similarly, IPD 16 may determine at 506 that an HV backup device isconsidered available, when in reality, no device can be relied upon todeliver an HV shock, which may result in IPD 16 continuing to enabledelivery of ATP therapy, even though no HV backup device is available todeliver an HV shock. However, despite the potential for inaccurateassessments by IPD 16, including inaccurate assessments as to theavailability of an HV backup device, such assessments may still besufficiently accurate to improve cardiac therapy significantly,particularly where the limitations of IPD 16 in making accurateassessments are understood and addressed.

FIG. 9 is a flow diagram illustrating an example process of a system inaccordance with one or more aspects of the present disclosure. Forpurposes of illustration, FIG. 9 is described below within the contextof operations performed by IPD 16 of FIG. 1 and FIG. 4. FIG. 9illustrates an example process for enabling and disabling delivery ofATP therapy in an example IPD 16. In the example described in connectionwith FIG. 9, the example IPD 16 may have capabilities for delivering ATPtherapy, but might not have capabilities for delivering ananti-tachyarrhythmia shock (HV shock).

In the example of FIG. 9, a timer may be used in making an assessment ofwhether an HV backup device is considered available to deliver an HVshock if appropriate. In a system such as that of FIG. 1, a clinicianmay make an initial or periodic determination of whether a device, suchas ICD system 30, is capable of delivering an HV shock. The clinicianmay make this determination based on an assessment of ICD system 30,which may include evaluating the age, condition, or battery liferemaining in ICD 9 of ICD system 30. Using this information, theclinician may send a signal to IPD 16, and responsive to this signal,IPD 16 may determine how long it might be able to rely on ICD system 30to serve as an HV backup device. The signal sent by the clinician to IPD16 may include information including a specific amount of time that ICDsystem 30 can be relied upon, based on the clinician's assessment. Inother examples, the signal may include information that processingcircuitry 90 within IPD 16 can use to determine an appropriate amount oftime during which ICD system 30 can be relied upon as an HV backupdevice capable of delivering an HV shock. The clinician may make thisdetermination periodically, and may send additional signals to IPD 16following subsequent determinations. Although certain aspects of FIG. 9may be described in terms of a person such as a clinician performingcertain operations, in other examples, another person, including patient14, may perform such operations. In still other examples, suchoperations may be performed by a computer, appliance, or other device,which may operate autonomously, or may be operated by a person.

With reference to FIG. 9, processing circuitry 90 within IPD 16 maydetect an enable event (602). As described above, the enable event maybe detected by IPD 16 following a signal sent by a clinician based on anassessment of ICD system 30. In other examples, the enable event mayinclude any of the example enable events described in connection withFIG. 8, including a signal that may originate from an internal device oran external device, or based on input from circuitry or modules withinIPD 16. Responsive to detecting the enable event, processing circuitry90 within IPD 16 may enable delivery of ATP therapy (604), such as inthe manner described in connection with FIG. 8.

After enabling delivery of ATP therapy, IPD 16 may determine whetheranother device capable of delivering an HV shock, such as ICD system 30,is considered available. The process for making this determination may,in some examples, include the sub-process 620 in FIG. 9, although inother examples, the process for making this determination may includemore operations, less operations, or different operations. In someexamples, the sub-process 620 may correspond to the determination madein sub-process 520 in FIG. 8.

Still referring to FIG. 9, processing circuitry 90 within IPD 16 maystart a timer (606) that may be used in making a determination ofwhether an HV backup device capable of delivering an HV shock isconsidered available. Processing circuitry 90 may monitor the timer anddetermine whether the time elapsed has reached a time limit (608). Insome examples, the time limit may be based on input received byprocessing circuitry 90 from communication circuitry 94. In someexamples, communication circuitry 94 may detect a signal correspondingto an enable event, such as a signal sent by a clinician, and output toprocessing circuitry 90 an indication of the signal received. In otherexamples, the time limit may be based on other information available toprocessing circuitry 90, including input from signal generationcircuitry 96, sensing circuitry 98, shock detection circuitry 99,activity sensor 100, or memory 92.

Before the time limit is reached, IPD 16 may also detect another enableevent (610), which may cause processing circuitry 90 to reset the timer(612) so that in some examples, the timer starts again with zero elapsedtime. Detecting an enable event in such a situation may be the result ofcommunication circuitry 94 receiving a signal from external device 21operated by a clinician during a clinician's periodic assessment of HVbackup devices in cardiac system 8, such as ICD system 30.

Until processing circuitry 90 detects that the timer has reached thetime limit, delivery of ATP may continue to be enabled. In someexamples, the time limit may be chosen to provide a higher degree ofcertainty that an HV backup device is available until the timer reachesthe time limit. This may include setting a time limit relatively low, sothat ICD system 30 is not likely to fail due to limited battery life orother issues before the time limit is reached. Where a new assessment ofthe capabilities of ICD system 30 can be made frequently, using a timelimit set relatively low may be appropriate in some examples. In otherexamples, the time limit may be fixed, or may change in response toprocessing circuitry 90 receiving input from signal generation circuitry96, sensing circuitry 98, shock detection circuitry 99, activity sensor100, or memory 92.

If processing circuitry 90 detects that the elapsed time has reached thelimit, IPD 16 may disable delivery of ATP. As described in connectionwith FIG. 8, disabling delivery of ATP may, in some examples, includeprocessing circuitry 90 outputting to signal generation circuitry 96information that causes signal generation circuitry 96 to disabledelivery of ATP, or in other examples, may include processing circuitry90 controlling signal generation circuitry 96 in such a way that resultsin disabling delivery of ATP. In accordance with one or more aspects ofthe present disclosure, disabling ATP may prevent delivery of ATP whenan HV backup device is not available.

FIG. 10A and FIG. 10B are flow diagrams illustrating example processesof a system in accordance with one or more aspects of the presentdisclosure. For purposes of illustration, FIG. 10A and FIG. 10B aredescribed below within the context of operations performed by IPD 16 ofFIG. 1 and FIG. 4. FIG. 10A and FIG. 10B illustrate example processesfor enabling and disabling delivery of ATP therapy in an example IPD 16.In the examples described in connection with FIG. 10A and FIG. 10B, theexample IPD 16 may have capabilities for delivering ATP therapy, butmight not have capabilities for delivering an anti-tachyarrhythmia shock(HV shock).

In the examples of FIG. 10A and FIG. 10B, IPD 16 may monitor cardiactherapy activity of cardiac system 8 to make an assessment of whether anHV backup device is considered available to deliver an HV shock ifappropriate. In example systems such as those described in connectionwith FIG. 10A and FIG. 10B, IPD 16 may independently monitor cardiactherapy activity, including therapy delivered by ICD system 30 or by anyother device included within cardiac system 8. Based on informationdetermined from such monitoring, IPD 16 may be able to determine whetheran HV backup device is considered available.

With reference to FIG. 10A, processing circuitry 90 within IPD 16 maydetect an enable event (702). The enable event may include any of theexamples described in connection with FIG. 8 or FIG. 9, including asignal that may originate from an internal device or an external device,or based on input to processing circuitry 90 from circuitry or moduleswithin IPD 16. Responsive to detecting the enable event, processingcircuitry 90 within IPD 16 may enable delivery of ATP therapy (704), asdescribed in connection with FIG. 8 and FIG. 9.

After enabling delivery of ATP therapy, IPD 16 may determine whetheranother device capable of delivering an HV shock, such as ICD system 30,is considered available. The process for making this determination may,in some examples, include the sub-process 720 in FIG. 10A, although inother examples, the process for making this determination may includemore operations, less operations, or different operations. In someexamples, the sub-process 720 a may correspond to sub-process 520 inFIG. 8.

Still referring to FIG. 10A, IPD 16 monitors cardiac therapy of cardiacsystem 8 (706). This may include sensing circuitry 98 within IPD 16detecting signals or voltage levels via electrode 52 and electrode 60,such as might occur if ICD system 30 were to deliver an HV shock duringthe course of delivering cardiac therapy to patient 14. Sensingcircuitry 98 may also monitor other activity of cardiac system 8 bydetecting signals or voltage levels via electrode 52 and electrode 60.

Responsive to detecting such signals or voltage levels, sensingcircuitry 98 may output to shock detection circuitry 99 an indication ofsignals sensed at electrode 52 and electrode 60. Also responsive to suchsignals, sensing circuitry 98 may output to processing circuitry 90 anindication of signals sensed at electrode 52 and electrode 60. Shockdetection circuitry 99 may also provide input to processing circuitry 90that includes information about the input from m98 based on the signalssensed at electrode 52 and electrode 60. Shock detection circuitry 99may be configured to detect cardiac therapy activity and output toprocessing circuitry 90 information about the detected cardiac therapyactivity. Responsive to receiving an indication of signals sensed,and/or responsive to receiving input from sensing circuitry 98 or shockdetection circuitry 99, processing circuitry 90 may determineinformation about cardiac therapy activity in cardiac system 8.Processing circuitry 90 uses this information to determine whether an HVbackup device, such as ICD system 30, is available (or no longeravailable) to deliver an HV shock (708). In this way, IPD 16 maycontinue to monitor cardiac therapy activity of cardiac system 8 (706)in the example shown. If processing circuitry 90 within IPD 16determines that the monitored cardiac therapy activity suggests that theHV backup device, such as ICD system 30, may no longer be available, IPD16 may disable delivery of ATP (718), which may include processingcircuitry 90 within IPD 16 disabling delivery of ATP as previouslydescribed in connection with FIG. 8 or FIG. 9, and in accordance withone or more aspects of this disclosure.

Referring now to FIG. 10B, sub-process 720 a in FIG. 10A has beenreplaced in FIG. 10B with an example sub-process 720 b that illustratesIPD 16 monitoring cardiac activity for one or more specific events. Inthe example of FIG. 10B, IPD 16 monitors for HV events in cardiac system8, which may be delivered by ICD system 30. In some examples, such aswhen ICD 9 within ICD system 30 is powered by a battery, ICD system 30may have the capability of delivering only a limited number of HVshocks, since each HV shock may diminish remaining battery life. If ICDsystem 30 delivers a sufficient number of HV shocks, ICD system 30 mayreach a state where it no longer has adequate battery power to reliablydeliver another HV shock. If ICD system 30 is unable to deliver an HVshock, it may be appropriate to disable delivery of ATP therapy.

In the example of FIG. 10B, each time IPD 16 detects an HV event (710),processing circuitry 90 within IPD 16 may increment a counter (712)within processing circuitry 90 to keep track of information relevant tobattery life for ICD system 30. The counter may, in some examples, beimplemented as part of the timing and control module of processingcircuitry 90. Until processing circuitry 90 detects that a thresholdnumber of HV events have been detected, delivery of ATP may continue tobe enabled (NO path from 716). In some examples, the threshold number ofHV events may be a predetermined number, which may be based on the typeor capabilities of the HV backup device being monitored. Once asufficient number of HV events are detected by processing circuitry 90,processing circuitry 90 may determine that ICD system 30 no longer hassufficient battery life to be relied upon as an HV backup device (716).Responsive to such a determination, IPD 16 may disable delivery of ATP(718).

In other examples, processing circuitry 90 may use information beyondsimply a count of HV events to determine whether ICD system 30 may ormay not have sufficient battery life to be relied upon as an HV backupdevice. Such information may include information about the voltagelevels or waveform associated with HV events detected in the system, orinformation about the time period in which HV events were detected, orinformation about other events detected in the system.

Also, in some examples, when IPD 16 detects delivery of an HV shock, IPD16 may adjust cardiac therapy following the delivery of the HV shock,such as by withholding ATP therapy (712). Withholding ATP delivery inthis manner may be temporary in some examples, and may not disabledelivery of ATP therapy. In other examples, IPD 16 may deliverpost-shock therapy after detecting an HV event.

In the example of FIG. 10B, IPD 16 may monitor for HV events in cardiacsystem 8 in an attempt to determine capabilities and remaining batterylife of ICD system 30, but IPD 16 might not receive any directcommunications from ICD system 30. In fact, in some examples, IPD 16might not be able to verify or confirm that any given HV shock was infact delivered by ICD system 30, as opposed to another device. But suchverification or confirmation may not be necessary. For example, in asystem where it is known that only one device has the capability fordelivering an HV shock, if an HV shock is detected by IPD 16, processingcircuitry 90 within IPD 16 might justifiably conclude that the HV shockwas delivered by ICD system 30.

Further, even in a system where there may be more than one possiblesource for an HV shock, processing circuitry 90 may be able to determinethat some percentage of any HV shocks detected by IPD 16 were actuallydelivered by ICD system 30. Processing circuitry 90 may make such adetermination based on input, received by processing circuitry 90, thatincludes information about cardiac system 8 or devices included incardiac system 8. Processing circuitry 90 may also make such adetermination based on detected cardiac therapy activity, which mayinclude information detected by sensing circuitry 98 that enablesprocessing circuitry 90 to distinguish between HV shocks delivered byICD system 30 and those delivered by another device.

Accordingly, in some examples where formal or informal communicationbetween IPD 16 and other devices within a system is limited, IPD 16 maystill be able to monitor cardiac therapy and derive useful informationabout the activity or condition of other devices within the system. Suchinformation may be sufficient to enable processing circuitry 90 withinIPD 16 to make sufficiently accurate determinations about remainingbattery life for ICD system 30 or another potential backup HV device.

FIG. 11 is a flow diagram illustrating an example process of a system inaccordance with one or more aspects of the present disclosure. Forpurposes of illustration, FIG. 11 is described below within the contextof operations performed by IPD 16 of FIG. 1 and FIG. 4. FIG. 11illustrates an example process for enabling and disabling delivery ofATP therapy in an example IPD 16. In the example described in connectionwith FIG. 11, the example IPD 16 may have capabilities for deliveringATP therapy, but might not have capabilities for delivering ananti-tachyarrhythmia shock (HV shock).

With reference to FIG. 11, processing circuitry 90 within IPD 16 maydetect an enable event (802), and responsive to detecting the enableevent, processing circuitry 90 within IPD 16 may enable delivery of ATPtherapy (804). In the example of FIG. 11, after enabling delivery ofATP, IPD 16 may monitor cardiac therapy activity and may also employs atimer to determine whether an HV backup device should be consideredavailable to deliver an HV shock if appropriate. As long as an HV backupdevice is considered available, ATP therapy may continue to be enabled;otherwise, ATP therapy may be disabled.

At 806 in FIG. 11, processing circuitry 90 within IPD 16 may start atimer and monitor the elapsed time until the elapsed time reaches thetime limit (808). If IPD 16 detects another enable event (810) beforethe timer reaches the time limit, the timer may be reset so that in someexamples, the elapsed time is reset to zero (812). IPD 16 may alsomonitor for HV events in cardiac system 8 (814). When an HV event isdetected (YES path from 814), IPD 16 may withhold ATP therapy in someexamples (816). IPD 16 may increment an HV counter when it detects an HVevent (818), and IPD 16 may monitor the HV counter to detect whether alimit, which may suggest that an HV backup device can no longer berelied upon, has been reached (819). IPD 16 may continue to monitorelapsed time and HV events until the timer reaches the time limit (YESpath from 808), or until the HV counter has reached its limit (YES pathfrom 819). If IPD 16 detects either condition, IPD 16 may disabledelivery of ATP therapy.

In some examples, IPD 16 may detect a re-enabling event, which may causeIPD 16 to enable delivery of ATP therapy (YES path from 824). In someexamples, IPD 16 may detect a re-enabling event as the result of aclinician sending a signal to IPD 16. In other examples, IPD 16 maydetect a re-enabling event as a result of another device, which mayinclude an HV backup device, sending a signal to IPD 16. In stillfurther examples, IPD 16 may detect a re-enable event based cardiactherapy activity detected by IPD 16, or based on input from sensingcircuitry 98, signal generation circuitry 96, shock detection circuitry99, or activity sensor 100. In still other examples, a re-enable eventmay be detected based on logic within processing circuitry 90 or basedon processing circuitry 90 executing instructions stored in memory 92.

In some examples, memory 92 may store parameters that may be used by IPD16 in a process such as that described in connection with FIG. 11. Suchparameters may include, but are not limited to, the amount of timeelapsed, information relating to the timer limit, parameters fordetermining how to adjust the timer limit based on cardiac therapydetected, the number of HV shocks detected, and information relating toa any limit on HV shocks.

FIG. 12 is a flow diagram illustrating an example process of a system inaccordance with one or more aspects of the present disclosure. Forpurposes of illustration, FIG. 12 is described from three differentperspectives, each relating to an example system such as cardiac system8 shown in FIG. 1. The first perspective (along the left side of line900 in FIG. 12) may be that of a clinician that may operate externaldevice 21, which may be used to send information to, or receiveinformation from, an ATP-capable device, such as IPD 16. External device21 may also communicate with other devices within cardiac system 8. Thesecond perspective (between lines 900 and 901 in FIG. 12) may be that ofan ATP capable device, such as IPD 16. The third perspective (along theright side of line 901 in FIG. 12) may be that of an HV capable device,or HV backup device, such as ICD system 30 including ICD 9. FIG. 12illustrates an example process for performing operations includingenabling and disabling delivery of ATP therapy in an example cardiacsystem 8. In the example described in connection with FIG. 12, theexample IPD 16 may have capabilities for delivering ATP therapy, butmight not have capabilities for delivering an anti-tachyarrhythmia shock(HV shock). Further, the example ICD system 30 may have capabilities fordelivering an HV shock, but might not have capabilities for deliveringATP therapy.

Referring to FIG. 12, a clinician may perform an evaluation (902) ofpatient 14 and/or cardiac system 8 to determine whether it isappropriate to enable delivery of ATP in IPD 16 (904). The clinician mayperform such an evaluation, and if delivery of ATP should be enabled,external device 21 may send an enable command to IPD 16 (906).Clinicians or other personnel (including patient 14) may periodicallyperform such assessments or evaluations (902) and when appropriate, useexternal device 21 or a similar device to send enable or re-enablecommands to IPD 16 (906). In some examples, a clinician or externaldevice 21 may perform an evaluation in response to receiving a disablealert from IPD 16 (908).

Referring now to the middle column of FIG. 12, IPD 16 may detect anenable event received from external device 21 (932), and responsive todetecting the enable event, IPD 16 may enable delivery of ATP (934). IPD16 may then perform operations to determine whether an HV backup devicecan still be considered available to deliver an HV shock (936). Suchoperations may be similar to those previously described in connectionwith sub-processes 520, 620, 720 a, 720 b, and 820 in FIG. 8, FIG. 9,FIG. 10A, FIG. 10B, and FIG. 11. Delivery of ATP may remain enableduntil IPD 16 determines that an HV backup device can no longer beconsidered available. Responsive to such a determination, IPD 16 maydisable delivery of ATP (938). In some examples, IPD 16 may send adisable alert, which may include sending or setting an alert forevaluation by a clinician (940).

Referring now to the right-hand column of FIG. 12, ICD system 30 mayoperate autonomously until processing circuitry 70 within ICD system 30determines that HV therapy may be required or desirable (952).Processing circuitry 70 may make this determination based on input fromsensing circuitry 78, activity sensor 82, signal generation circuitry76, communications circuitry 80, or from another source, or based onlogic within processing circuitry 70. When appropriate, ICD system 30may deliver cardiac therapy through signal generation circuitry 76and/or shock circuitry 75. The cardiac therapy delivered by ICD system30 may include an HV shock (954). In FIG. 12, arrow 960 may indicatethat IPD 16 monitors such therapy and may use information about themonitored therapy to make an assessment at 936.

In some examples, communications circuitry 80 within ICD system 30 maydetect an enable command or information about an enable command sent byexternal device 21 (906 and 920). Responsive to receiving the enablecommand or information about an enable command, ICD system 30 may alterits operation. See FIG. 12 Similarly, communications circuitry 80 withinICD system 30 may detect a disable alert or information about a disablealert sent by IPD 16 (940 and 950). Responsive to receiving the disablealert or information about the disable alert, ICD system 30 may alterits operation. See FIG. 12

Techniques in accordance with the present disclosure may includedisabling delivery of ATP therapy in an otherwise ATP-capable device. Adevice that is configured to deliver ATP therapy, but that in somecircumstances does not deliver ATP therapy, may perform fewer operationsand deliver fewer pacing signals to a patient's heart. As a result, sucha device may consume less electrical power.

In some examples, the operations shown or described in flow diagrams maybe performed in a different order or presented in a different sequence,but still be in accordance with one or more aspects of the presentdisclosure. Also, while certain operations may be presented in aparticular sequence, in other examples, operations may be performed inparallel or substantially parallel, yet still be in accordance with oneor more aspects of the present disclosure. Further, a process ortechnique in accordance with one or more aspects of the presentdisclosure may be implemented with less than the operations shown ordescribed, and in other examples, such a process may be implemented withmore than the operations shown or described.

Any suitable modifications may be made to the processes described hereinand any suitable device, processing circuitry, therapy deliverycircuitry, and/or electrodes may be used for performing the steps of themethods described herein. The steps the methods may be performed by anysuitable number of devices. For example, a processing circuitry of onedevice may perform some of the steps while a therapy delivery circuitryand/or sensing circuitry of another device may perform other steps ofthe method, while communication circuitry may allow for communicationneeded for the processing circuitry to receive information from otherdevices. This coordination may be performed in any suitable manneraccording to particular needs.

The disclosure contemplates computer-readable storage media comprisinginstructions to cause a processor to perform any of the functions andtechniques described herein. The computer-readable storage media maytake the example form of any volatile, non-volatile, magnetic, optical,or electrical media, such as a RAM, ROM, NVRAM, EEPROM, or flash memory.The computer-readable storage media may be referred to asnon-transitory. A programmer, such as patient programmer or clinicianprogrammer, or other computing device may also contain a more portableremovable memory type to enable easy data transfer or offline dataanalysis.

The techniques described in this disclosure, including those attributedto ICD system 30, IPD 16, external device 21, and various constituentcomponents, may be implemented, at least in part, in hardware, software,firmware or any combination thereof. For example, various aspects of thetechniques may be implemented within one or more processors, includingone or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalentintegrated or discrete logic circuitry, as well as any combinations ofsuch components, embodied in programmers, such as physician or patientprogrammers, stimulators, remote servers, or other devices. The term“processor” or “processing circuitry” may generally refer to any of theforegoing logic circuitry, alone or in combination with other logiccircuitry, or any other equivalent circuitry.

Such hardware, software, firmware may be implemented within the samedevice or within separate devices to support the various operations andfunctions described in this disclosure. For example, any of thetechniques or processes described herein may be performed within onedevice or at least partially distributed amongst two or more devices,such as between ICD system 30, IPD 16, and/or external device 21. Inaddition, any of the described units, modules or components may beimplemented together or separately as discrete but interoperable logicdevices. Depiction of different features as modules or units is intendedto highlight different functional aspects and does not necessarily implythat such modules or units must be realized by separate hardware orsoftware components. Rather, functionality associated with one or moremodules or units may be performed by separate hardware or softwarecomponents, or integrated within common or separate hardware or softwarecomponents.

The techniques described in this disclosure may also be embodied orencoded in an article of manufacture including a non-transitorycomputer-readable storage medium encoded with instructions. Instructionsembedded or encoded in an article of manufacture including anon-transitory computer-readable storage medium encoded, may cause oneor more programmable processors, or other processors, to implement oneor more of the techniques described herein, such as when instructionsincluded or encoded in the non-transitory computer-readable storagemedium are executed by the one or more processors. Examplenon-transitory computer-readable storage media may include random accessmemory (RAM), read only memory (ROM), programmable read only memory(PROM), erasable programmable read only memory (EPROM), electronicallyerasable programmable read only memory (EEPROM), flash memory, a harddisk, a compact disc ROM (CD-ROM), a floppy disk, a cassette, magneticmedia, optical media, or any other computer readable storage devices ortangible computer readable media.

As used herein, the term “circuitry” refers to an application specificintegrated circuit (ASIC), an electronic circuit, a processor (shared,dedicated, or group) and memory that execute one or more software orfirmware programs, a combinational logic circuit, or other suitablecomponents that provide the described functionality.

In some examples, a computer-readable storage medium comprisesnon-transitory medium. The term “non-transitory” may indicate that thestorage medium is not embodied in a carrier wave or a propagated signal.In certain examples, a non-transitory storage medium may store data thatcan, over time, change (e.g., in RAM or cache).

Various examples have been described for delivering cardiac stimulationtherapies as well as coordinating the operation of various deviceswithin a patient. Any combination of the described operations orfunctions is contemplated. These and other examples may be within thescope of the following claims.

What is claimed is:
 1. A method comprising: detecting, by an implantablemedical device configured to deliver anti-tachyarrhythmia pacing (ATP)to a heart of a patient, an enable event; responsive to detecting theenable event, enabling, by the implantable medical device, the deliveryof ATP; responsive to detecting the enable event, starting, by theimplantable medical device, a timer; detecting, by the implantablemedical device, a disable event indicating that another implantablemedical device cannot be relied upon to deliver an anti-tachyarrhythmiashock, wherein detecting the disable event comprises detecting that thetimer has reached a time limit without requiring communication betweenthe implantable medical device and the other implantable medical device;and responsive to detecting the disable event, disabling, by theimplantable medical device, delivery of ATP.
 2. The method of claim 1,wherein detecting the enable event comprises receiving, by theimplantable medical device, an enable signal from an external device viawireless communication.
 3. The method of claim 1, wherein the enableevent is a first enable event, further comprising: detecting, by theimplantable medical device after starting the timer, a second enableevent; and responsive to detecting the second enable event, restarting,by the implantable medical device, the timer.
 4. The method of claim 3,wherein detecting the second enable event comprises detecting the secondenable event after disabling the delivery of ATP, the method furthercomprising, responsive to detecting the second enable event, enabling,by the implantable medical device, delivery of ATP.
 5. The method ofclaim 1, wherein the implantable medical device comprises anintracardiac pacemaker configured for implantation in the heart, andwherein the other implantable medical device comprises anextracardiovascular implantable cardiac defibrillator configured forextracardiovascular implantation in the patient.
 6. The method of claim1, further comprising: responsive to detecting the disable event,generating, by the implantable medical device, a disable alert.
 7. Amethod comprising: detecting, by an implantable medical deviceconfigured to deliver anti-tachyarrhythmia pacing (ATP) to a heart of apatient, an enable event; responsive to detecting the enable event,enabling, by the implantable medical device, the delivery of ATP;responsive to detecting the enable event, starting, by the implantablemedical device, a timer; detecting, by the implantable medical device, adisable event indicating that another implantable medical device cannotbe relied upon to deliver an anti-tachyarrhythmia shock, whereindetecting the disable event comprises detecting that the timer hasreached a time limit; responsive to detecting the disable event,disabling, by the implantable medical device, delivery of ATP;detecting, by the implantable medical device via a plurality ofelectrodes, cardiac therapy activity; and modifying, by the implantablemedical device, the timer based on detection of the cardiac therapyactivity.
 8. The method of claim 7, wherein detecting the enable eventcomprises detecting, by the implantable medical device, a signal,wherein the signal is generated by the other implantable medical device.9. The method of claim 8, wherein detecting the enable event comprisesdetecting the signal via wireless communication.
 10. The method of claim7, wherein detecting the cardiac therapy activity comprises detectingdelivery of one or more anti-tachyarrhythmia shocks, and whereinmodifying the timer comprises shortening the time limit in response todetecting the delivery of the one or more anti-tachyarrhythmia shocks.11. A method comprising: detecting, by an implantable medical deviceconfigured to deliver anti-tachyarrhythmia pacing (ATP) to a heart of apatient, an enable event; responsive to detecting the enable event,enabling, by the implantable medical device, the delivery of ATP;detecting, by the implantable medical device, a disable event indicatingthat another implantable medical device cannot be relied upon to deliveran anti-tachyarrhythmia shock, wherein detecting the disable eventcomprises detecting delivery of a threshold number ofanti-tachyarrhythmia shocks, thereby suggesting that the otherimplantable medical device cannot be relied upon to deliver ananti-tachyarrhythmia shock; and responsive to detecting the disableevent, disabling, by the implantable medical device, delivery of ATP.